Yemen: Civil War and Regional Intervention

Updated March 21, 2019 (R43960)
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This report provides information on the ongoing crisis in Yemen. Now in its fifth year, the war in Yemen shows no signs of abating. The war has killed thousands of Yemenis, including combatants as well as civilians, and has significantly damaged the country's infrastructure. The difficulty of accessing certain areas of Yemen has made it problematic for governments and aid agencies to count the war's casualties. One U.S. and European-funded organization, the Armed Conflict Location & Event Data Project (ACLED), estimates that 60,000 Yemenis have been killed since January 2016.

Though fighting continues along several fronts, on December 13, 2018, Special Envoy of the United Nations Secretary-General for Yemen Martin Griffiths brokered a cease-fire centered on the besieged Red Sea port city of Hudaydah, Yemen's largest port. As part of the deal, the coalition and the Houthis agreed to redeploy their forces outside Hudaydah city and port. The United Nations agreed to chair a Redeployment Coordination Committee (RCC) to monitor the cease-fire and redeployment. On January 16, the United Nations Security Council (UNSCR) passed UNSCR 2452, which authorized (for a six-month period) the creation of the United Nations Mission to support the Hudaydah Agreement (UNMHA), of which the RCC is a significant component. As of late March 2019, the Stockholm Agreement remains unfulfilled, although U.N. officials claim that the parties have made "significant progress towards an agreement to implement phase one of the redeployments of the Hudayda agreement."

Although both the Obama and Trump Administrations have called for a political solution to the conflict, the two sides in Yemen appear to fundamentally disagree over the framework for a potential political solution. The Saudi-led coalition demands that the Houthi militia disarm, relinquish its heavy weaponry (ballistic missiles and rockets), and return control of the capital, Sanaa, to the internationally recognized government of President Abdu Rabbu Mansour Hadi, who is in exile in Saudi Arabia. The coalition asserts that there remains international consensus for these demands, insisting that the conditions laid out in United Nations Security Council Resolution (UNSCR) 2216 (April 2015) should form the basis for a solution to the conflict. The Houthis reject UNSCR 2216 and seem determined to outlast their opponents while consolidating their control over northern Yemen. Since the December 2017 Houthi killing of former President Ali Abdullah Saleh, a former Houthi ally, there is no apparent single Yemeni rival to challenge Houthi rule in northern Yemen. Armed groups, including Islamist extremists, operate in other parts of the country, and rival political movements and trends advance competing visions for the long-term reestablishment of national governance in the country. The reconciliation of Yemeni factions and the redefinition of the country's political system, security sector, and social contract will likely require years of additional diplomatic engagement.

According to the United Nations, Yemen's humanitarian crisis is the worst in the world, with close to 80% of Yemen's population of nearly 30 million needing some form of assistance. Two-thirds of the population is considered food insecure; one-third is suffering from extreme levels of hunger; and the United Nations estimates that 230 out of Yemen's 333 districts are at risk of famine. In sum, the United Nations notes that humanitarian assistance is "increasingly becoming the only lifeline for millions of Yemenis."

For additional information on Yemen, including a summary of relevant legislation, please see CRS Report R45046, Congress and the War in Yemen: Oversight and Legislation 2015-2019, by Jeremy M. Sharp and Christopher M. Blanchard.


Central governance in Yemen, embodied by the decades-long rule of former President Ali Abdullah Saleh, began to unravel in 2011, when political unrest broke out throughout the Arab world. Popular youth protests in Yemen were gradually supplanted by political elites jockeying to replace then-President Saleh. Ultimately, infighting among various centers of Yemeni political power broke out in the capital, and government authority throughout the country eroded. Soon, militias associated with Al Qaeda in the Arabian Peninsula (AQAP) seized territory in one southern province. Concerned that the political unrest and resulting security vacuum were strengthening terrorist elements, the United States, Saudi Arabia, and other members of the international community attempted to broker a political compromise. A transition plan was brokered, and in 2012 former Vice President Abdu Rabbu Mansour Hadi became president.

With the support of the United States, Saudi Arabia, and the United Nations Security Council, President Hadi attempted to reform Yemen's political system. Throughout 2013, key players convened a National Dialogue Conference aimed at reaching broad national consensus on a new political order. However, in January 2014 it ended without agreement.

One antigovernment group in particular, the northern Yemeni Houthi movement, sought to use military force to reshape the political order. Within weeks of the National Dialogue Conference concluding, it launched a military offensive against various tribal allies of President Hadi. The Houthi were joined by the forces still loyal to former President Saleh, creating an alliance of convenience that was a formidable opponent to President Hadi and his allies.

Who are the Houthis?

The Houthi movement (also known as Ansar Allah or Partisans of God) is a predominantly Zaydi Shiite revivalist political and insurgent movement. Yemen's Zaydis take their name from their fifth Imam, Zayd ibn Ali, grandson of Husayn. Zayd revolted against the Umayyad Caliphate in 740, believing it to be corrupt, and to this day, Zaydis believe that their imam (ruler of the community) should be both a descendent of Ali (the cousin and son-in-law of the prophet Muhammad) and one who makes it his religious duty to rebel against unjust rulers and corruption. A Zaydi state (or Imamate) was founded in northern Yemen in 893 and lasted in various forms until the republican revolution of 1962. Yemen's modern imams kept their state in the Yemeni highlands in extreme isolation, as foreign visitors required the ruler's permission to enter the kingdom. Although Zaydism is an offshoot of Shia Islam, its legal traditions and religious practices are similar to Sunni Islam. Zaydism is doctrinally distinct from "Twelver Shiism," the dominant branch of Shia Islam in Iran and Lebanon.

The Houthi movement was formed in the northern Yemeni province of Sa'dah (in the mountainous district of Marran) in 2004 under the leadership of members of the Houthi family. Between 2004 and 2010, the central government and the Houthis fought six wars in northern Yemen. With each successive round of fighting, the Houthis improved their position, as anti-government sentiment became more widespread amidst an aggrieved population in a war-torn and neglected north. Although the Houthi movement originally sought an end to what it viewed as efforts to marginalize Zaydi communities and beliefs, its goals grew in scope and ambition in the wake of the 2011 uprising and government collapse to embrace a broader populist, anti-establishment message. Ideologically, the group has espoused anti-American and anti-Zionist beliefs, embodied by the slogans prominently displayed on its banners: "God is great! Death to America! Death to Israel! Curse the Jews! Victory to Islam!"

In 2014, Houthi militants took over the capital of Sanaa (also spelled Sana'a) and violated several power-sharing arrangements. In 2015, Houthi forces advanced southward from the capital all the way to Aden on the Arabian Sea. In March 2015, after President Hadi, who had fled to Saudi Arabia, appealed for international intervention, Saudi Arabia and a hastily assembled international coalition launched a military offensive aimed at restoring Hadi's rule and evicting Houthi fighters from the capital and other major cities.

Table 1. Yemen Timeline

Select events 2015-2018




March 23: After capturing the capital Sanaa in September 2014, Houthi-Saleh forces seize control over most of Aden. President Hadi flees to Saudi Arabia seeking international assistance.



March 26: The Saudi-led coalition begins military operations with air strikes against Houthi-Saleh forces.



July – August: The Saudi-led coalition retakes Aden.



September – October: Houthi-Saleh forces fire a ballistic missile at a military base used by UAE forces, killing at least 45 UAE soldiers and 5 Bahraini troops. Saudi-led coalition airstrikes hit two separate wedding parties, killing at least 81 people in one and 23 in another.



December: U.N.negotiates a temporary cease-fire, as UN-mediated peace talks begin in Switzerland. The cease-fire lasts two weeks, ending in early January 2016.



March – October: Saudi-led coalition airstrikes target:

A market in northwestern Yemen, killing at least 97 civilians and 10 Houthi fighters

An MSF-supported hospital for the fourth time, killing 19

A funeral reception, killing 130-150, including many senior Houthi political and military figures



April – August: U.N.-brokered peace negotiations begin in Kuwait, but end in August with no agreement.



October: Houthi-Saleh forces launch anti-ship missiles at U.S. Navy vessels on patrol off the coast of Yemen, the first time U.S. Armed Forces come under direct fire in the war. The Obama Administration responds by directing the Armed Forces to fire cruise missiles against Houthi-Saleh radar installations in self-defense.



October 19: A 72-hour new cessation of hostilities goes into effect. Violations occur and the ceasefire lasts until October 23 without renewal.



November 4: After a Houthi-fired missile with alleged Iranian origins lands deep inside Saudi Arabia, the coalition institutes a full blockade of all of Yemen's ports, including the main port of Hudaydah (also spelled Hodeidah, Hudayda), exacerbating the country's humanitarian crisis.



December 4: The Houthi-Saleh alliance unravels, culminating in the killing of former President Saleh on December 4, 2017 by Houthi rebels near the capital Sanaa.



June: Saudi-led coalition launches Operation Golden Victory with the aim of retaking the Red Sea port city of Hudaydah.



August: Saudi-led coalition airstrike hits a bus in a market near Dahyan, Yemen, in the northern Sa'dah governorate, killing 51 people, 40 of whom were children, allegedly in response to a Houthi missile attack on the Saudi city of Jizan a day earlier that killed a Yemeni national in the kingdom.



September: UN-mediated talks in Geneva last three days. The Houthi delegation never arrives, claiming it was prevented from traveling by the coalition. The coalition claims that the Houthis sabotaged the arrangements to facilitate their travel with new last minute demands.



November: Saudi-led coalition pauses military operations to pursue negotiations, having seized the eastern outskirts of Hudaydah, severing access to the main road leading eastward to the Houthi-controlled capital Sana'a.



December 13: After ten days of UN-mediated talks, the two parties announce the Stockholm Agreement, key components of which include a prisoner swap, a mutual redeployment of forces from Hudaydah, and the formation of a committee to discuss the contested city of Taiz.

Source: CRS Graphics.

In April 2015, the United Nations Security Council passed Resolution (UNSCR) 2216 demanding that Houthi-Saleh forces end their use of violence and that all Yemeni parties avoid "further unilateral actions that could undermine the political transition in Yemen." The United States agreed to provide limited assistance to the coalition military operations, assistance which has evolved over time in response to conditions in the conflict and in light of congressional scrutiny.

In early December 2017, the Houthi-Saleh alliance unraveled, culminating in the killing of former President Saleh on December 4, 2017. Since Saleh's death, the coalition has made military gains, advancing northward along the Red Sea coast toward the port of Hudaydah (also spelled Hodeidah, Hudayda). Nevertheless, Houthi forces remain ensconced in northern Yemen and remain in control of the capital.

The war has exacerbated a humanitarian crisis in Yemen that began in 2011; as of January 2019, over half of the population required emergency food assistance.1 Access restrictions to certain areas of Yemen make it problematic for governments and aid agencies to count the war's casualties. One U.S. and European-funded organization, the Armed Conflict Location & Event Data Project (ACLED), estimates that 60,000 Yemenis have been killed since January 2016.2 UNHCR estimates that 3.9 million Yemenis were displaced internally as of January 2019.3

In January 2019, the United Nations Panel of Experts on Yemen released their annual report covering 2018. This report noted that Yemen continues to "slide towards humanitarian and economic catastrophe."4 Though the actual ground war remains confined to "relatively small areas," the effect of the conflict on the economy, as well as the growing presence of armed groups and deep-rooted corruption, has impacted ordinary Yemenis within both Houthi-held areas and liberated areas.

Stockholm Agreement and Hudaydah Cease-Fire

On December 6, 2018, the warring parties to the conflict in Yemen convened in Sweden under the auspices of the United Nations to discuss various de-escalation proposals and a possible road map to a comprehensive peace settlement. The talks were the first formal negotiations since 2016. After a week of negotiations, all sides agreed to the Stockholm Agreement, which consists of three components: a cease-fire around the port city of Hudaydah, a prisoner swap, and a statement of understanding that all sides would form a committee to discuss the war-torn city Taiz.

Though fighting continues along several fronts, on December 13, 2018, Special Envoy of the United Nations Secretary-General for Yemen Martin Griffiths brokered a cease-fire centered on the besieged Red Sea port city of Hudaydah, Yemen's largest port.5 As part of the deal, the coalition and the Houthis agreed to redeploy their forces outside Hudaydah city and port. The United Nations agreed to chair a Redeployment Coordination Committee (RCC) to monitor the cease-fire and redeployment.

On January 16, the United Nations Security Council (UNSCR) passed UNSCR 2452, which authorized (for a 6-month period) the creation of the United Nations Mission to support the Hudaydah Agreement (UNMHA), of which the RCC was a significant component.6

For nearly two months, implementation of the Stockholm Agreement stalled. According to U.N. Special Envoy Griffiths, "The initial timelines were rather ambitious….We are dealing with a complex situation on the ground."7 The Stockholm Agreement did not specify which local actors were to assume responsibility for security in Hudaydah after both parties redeployed.8

On February 17, the United Nations announced that "The parties reached an agreement on Phase 1 of the mutual redeployment of forces" whereby the Houthis would withdraw from Hudaydah port and the Saudi-led coalition would move out of the eastern outskirts of Hudaydah city.9 Still, the warring parties have yet to agree on the identities of local police forces to take over security in Hudaydah.10 As of March 2019, the parties had made "significant progress towards an agreement to implement phase one of the redeployments of the Hudayda agreement."11

Until a final redeployment is reached, the Houthis remain ensconced in Hudaydah, with barricades, trenches and roadblocks still present throughout the city. The Houthis want local coast guard units to assume control. The coalition claims, however, that the leaders of the local coast guards are loyal to the Houthis, and U.N. observers may have difficulty in verifying the neutrality of security personnel in Hudaydah. U.N. officials have reported to the Security Council that the Houthis fear that a withdrawal from Hudaydah will make their forces vulnerable to attack by the coalition.12

Meanwhile, in Jordan, several meetings between the Houthis and the Hadi government have taken place over a planned prisoner exchange as called for in the Stockholm Agreement. Although some exchanges of wounded personnel and prisoners have taken place, the talks have not produced a comprehensive agreement to date.

Overall, many observers remain skeptical that the cease-fire reflects a broader impulse to end the war, seeing it instead as a means of easing international pressure on the coalition.13 Since the signing of the Stockholm Agreement, the Saudi-led coalition has conducted airstrikes in Sanaa in retaliation for a Houthi drone attack against a Yemeni military parade. In late January, artillery fire struck a camp for internally displaced people in Yemen's northwestern Hajjah province, killing eight civilians and wounding 30 others. According to reporting by the United Nations, implementation of the Stockholm Agreement has been hindered by an overall lack of trust and a reluctance to make operational concessions outside of a comprehensive political agreement.14

Figure 1. Lines of Control in Yemen

As of July 2018

Source: Graphic created by CRS. Map and information generated by Hannah Fischer using data from Risk Intelligence (2018); Esri (2017 & 2018); NOAA (2018); USGS (2018); Department of State (2015).

Recent U.S. Policy

In 2019, the Trump Administration has continued to support United Nations-led efforts in addressing the humanitarian situation and working toward a comprehensive peace in Yemen. At the same time, the United States has continued to cooperate with Saudi Arabia and the UAE in countering terrorism and attempting to limit Iran's influence in Yemen.15 For the Trump Administration, U.S. officials have supported the continued defense of Saudi Arabia against Houthi missile and rocket strikes, while also openly calling on coalition members to use air power judiciously to minimize civilian casualties. After ending U.S. refueling support at the coalition's request in November 2018, the Administration has argued against congressional attempts to block arms sales or to end or condition U.S. assistance, arguing that continued U.S. assistance is more likely to achieve the objectives of limiting civilian casualties and maintaining strategic ties to Gulf partners than a punitive approach.

To address congressional concerns16 over errant coalition airstrikes against Yemeni civilians, on November 11, 2018, the United States halted in-flight refueling support for coalition aircraft at the request of the coalition. A month later, then-U.S. Ambassador-designate to Yemen Christopher Henzel noted in his Senate confirmation hearing that

"At our urging, the Saudi-led coalition has incorporated the no-strike list into its target development procedures, stopped the use of cluster munitions, changed its rules of engagement to incorporate U.S. recommendations, and established the Joint Incident Assessment team. The United States will continue to press the coalition and the Republic of Yemen government to minimize civilian casualties and expand urgent humanitarian efforts throughout the country."17

In early February 2019, CENTCOM Commander General Joseph Votel testified before the Senate Armed Services Committee regarding the U.S. role in assisting Saudi Arabia. General Votel remarked that:

The United States will continue to support our regional partners developing processes and procedures to counter ballistic missiles (CBM) and counter unmanned armed aerial systems (C-UAS) to help mitigate threats to civilian populations and critical infrastructure…. We continue to share our own experiences and processes in an effort to improve Saudi Arabia's operational performance and reduce civilian casualties. CENTCOM's security cooperation with Saudi Arabia remains a critical link in our efforts to strengthen partners in the region and meet current and future challenges. The work of U.S. advisors is essential to the success of our mission, and Saudi Arabia underwrites the lion's share of their presence. 18

In February 2019, CNN reported that Saudi Arabia and the UAE had provided U.S. military equipment (armored vehicles) to local Yemeni units fighting the Houthis in possible violation of end-user foreign military sale or direct commercial sale agreements. The coalition has denied these charges, while the U.S. State Department has said that it is "seeking additional information" on the issue.19

At the February 2019 Ministerial to Promote a Future of Peace and Security in the Middle East in Warsaw, Poland, members of the self-described "quad" (United States, United Kingdom, Saudi Arabia, and the United Arab Emirates) met to coordinate their policy toward the Yemen conflict. The quad emphasized the importance of implementing the Stockholm Agreement, the problematic role Iran plays in arming and financing the Houthis, and the need for additional humanitarian assistance. The foreign ministers comprising the quad also "expressed full support for Saudi Arabia and its legitimate national security concerns and called for an immediate end to such attacks by Houthi forces and their allies."20

On February 13, 2019, the House passed (248-177) H.J.Res. 37, a joint resolution "Directing the removal of United States Armed Forces from hostilities in the Republic of Yemen that have not been authorized by Congress." Prior to its passage by the House, the White House issued a Statement of Administration Policy in which the Administration argued that "the premise of the joint resolution is flawed" because the United States has provided only "limited support to member countries of the Saudi-led coalition" and U.S. forces providing such intelligence and logistics support are not engaged in hostilities.21 As amended and passed by the House, Section 4 of H.J.Res. 37 includes a rule of construction stating that "Nothing in this joint resolution may be construed to influence or disrupt any intelligence, counterintelligence, or investigative activities conducted by, or in conjunction with, the United States Government…"

The Senate companion resolution, S.J.Res. 7, was introduced on January 30, 2019 and passed by the Senate (54-46) on March 13, 2019. As amended, S.J.Res. 7 includes rules of construction stating that "nothing in this joint resolution may be construed to influence or disrupt any intelligence, counterintelligence or investigative activities relating to threats in or emanating from Yemen conducted by, or in conjunction with, the United States Government…" (Section 4) and that "nothing in this joint resolution may be construed as authorizing the use of military force" (Section 7).

The War in Yemen: Have U.S. Forces Been Introduced into Hostilities?

There is some disagreement between some in Congress and the Trump Administration as to whether U.S. forces assisting the Saudi-led coalition have been introduced into active or imminent hostilities for purposes of the War Powers Resolution (50 U.S.C. Ch. 33). Some Members have claimed that by providing support to the Saudi-led coalition, U.S. forces have been introduced into a "situation where imminent involvement in hostilities is clearly indicated" based on the criteria of the War Powers Resolution. The Trump Administration disagrees. The U.S. Defense Department has maintained that "the limited military and intelligence support that the United States is providing to the KSA-led coalition does not involve any introduction of U.S. forces into hostilities for purposes of the War Powers Resolution." Both H.J.Res. 37 (passed 248-177 on February 13, 2019) and S.J.Res. 7 (passed 54-46 on March 13, 2019), direct the President to remove U.S. Armed Forces from hostilities "in or affecting the Republic of Yemen, except United States Armed Forces engaged in operations directed at Al Qaeda or associated forces." Section 1 of both joint resolutions as passed by the House and Senate respectively state: "Since March 2015, members of the United States Armed Forces have been introduced into hostilities between the Saudi-led coalition and the Houthis, including providing to the Saudi-led coalition aerial targeting assistance, intelligence sharing, and mid-flight aerial refueling." The joint resolutions specifically define the provision of aerial refueling as constituting hostilities for the purposes of the joint resolutions, reflecting a Senate-passed amendment to the version of the joint resolutions that the Senate passed in December 2018 (S.J.Res. 54).

On February 7, 2019, Ranking Member on the Senate Foreign Relations Committee Senator Robert Menendez introduced S. 398, the Saudi Arabia Accountability and Yemen Act of 2019. This bill, which was originally introduced in the 115th Congress, would, among other things, require the end of in-flight refueling for Saudi-led coalition operations in Yemen, suspend certain arms sales to the kingdom, sanction persons blocking humanitarian access in Yemen, and sanction persons supporting the Houthis in Yemen.

Iranian Support to the Houthis

Although Houthi militia forces most likely do not depend on Iran for all of their armaments, financing, and manpower, many observers agree that Iran22 and its Lebanese ally Hezbollah have aided Houthi forces with advice, training, and arms shipments.23 In 2016, one unnamed Hezbollah commander interviewed about his group's support for the Houthis remarked "After we are done with Syria, we will start with Yemen, Hezbollah is already there.... Who do you think fires Tochka missiles into Saudi Arabia? It's not the Houthis in their sandals, it's us."24 In repeated public statements by high-level Saudi officials, Saudi Arabia has cited Iran's illicit support for the Houthis as proof that Iran is to blame for the Yemen conflict. Reports and allegations of Iranian involvement in Yemen have become more frequent as the war has continued, and from Iran's perspective, aiding the Houthis would seem to be a relatively low-cost way of keeping Saudi Arabia mired in the Yemen conflict. However, Iran had few institutionalized links to the Houthis before the civil conflict broke out in 2015, and questions remain about the degree to which Iran and its allies can control or influence Houthi behavior. At present, Iranian aid to the Houthis does not appear to match the scale of its commitments to proxies in other parts of the Middle East, such as in Syria, Lebanon, and Iraq.

Prior to the 2015 conflict, the central government in Yemen had acquired variants of Scud-B missiles from the Soviet Union and North Korea. The Houthis took control of these missiles as part of their seizure of the capital. Since 2016, the Houthis have been firing what they call the "Burkan" short-range ballistic missile (claimed range of 500-620 miles) into Saudi Arabia (the latest version is the Burkan-2H). In November 2017, after the Houthis fired a Burkan-2H deep into Saudi Arabian territory, the Saudi-led coalition and U.S. officials said that the Burkan-2H is an Iran-manufactured Qaim missile.25

In January 2018, the United Nations Panel of Experts on Yemen concluded that Iran was in noncompliance with UNSCR 2216 for failing to prevent the transfer to Houthi forces of Iranian-made short-range ballistic missiles.26 On February 26, 2018, Russia vetoed a draft U.N. Security Council resolution that would have expressed U.N. concern that Iran is in noncompliance with the international arms embargo created by UNSCR 2216.

Figure 2. Houthi-Saleh Forces Display the "Burkan-2" Missile

Source: An image released by the pro Houthi-Saleh SABA News Agency on February 6, 2017, Jane's Defence Weekly, February 8, 2017.

In summer 2018, the United Nations Panel of Experts on Yemen provided a confidential report to the United Nations Security Council suggesting that Iran may be continuing to violate the international arms embargo by supplying the Houthis with advanced weaponry. After the U.N. experts visited Saudi Arabia and inspected debris from missiles fired by the Houthis, their report noted that these weapons showed "characteristics similar to weapons systems known to be produced in the Islamic Republic of Iran" and that there was a "high probability" that the missiles were manufactured outside of Yemen, shipped in sections to the country, and reassembled by the Houthis.27

In May 2018, the U.S. Department of the Treasury's Office of Foreign Assets Control (OFAC) designated five Iranian individuals who have "provided ballistic missile-related technical expertise to Yemen's Houthis, and who have transferred weapons not seen in Yemen prior to the current conflict, on behalf of the Islamic Revolutionary Guard Corps-Qods Force (IRGC-QF)."28

In testimony to the Senate Select Committee on Intelligence in January 2019, Director of National Intelligence Daniel Coats stated:

In Yemen, Iran's support to the Huthis, including supplying ballistic missiles, risks escalating the conflict and poses a serious threat to US partners and interests in the region. Iran continues to provide support that enables Huthi attacks against shipping near the Bab el Mandeb Strait and land-based targets deep inside Saudi Arabia and the UAE, using ballistic missiles and UAVs.29

The U.N. Panel of Experts on Yemen reported in January 2019 that the panel "has traced the supply to the Houthis of unmanned aerial vehicles and a mixing machine for rocket fuel and found that individuals and entities of Iranian origin have funded the purchase." 30

Saudi Arabia and U.S. Support for the Coalition

For Saudi Arabia, according to one prominent analyst, the Houthis embody what Iran seeks to achieve across the Arab world: that is, the cultivation of an armed nonstate, non-Sunni actor who can pressure Iran's adversaries both politically and militarily (akin to Hezbollah in Lebanon).31 A decade before the current conflict began in 2015, Saudi Arabia supported the central government of Yemen in various military campaigns against a Houthi insurgency which began in 2004.32

In 2014, when Houthi militants took over the capital and violated several power-sharing arrangements, Saudi leaders expressed increasing alarm about Houthi advances. In March 2015, after President Hadi, who had fled to Saudi Arabia, appealed for international intervention, Saudi Arabia quickly assembled an international coalition and launched a military offensive aimed at restoring Hadi's rule and evicting Houthi fighters from the capital and other major cities.33 Saudi-led coalition forces began conducting air strikes against Houthi-Saleh forces and imposed strict limits on sea and air traffic to Yemen.

From the outset, Saudi leaders sought material and military support from the United States for the campaign. In March 2015, President Obama authorized "the provision of logistical and intelligence support to GCC-led military operations," and the Obama Administration announced that the United States would establish "a Joint Planning Cell with Saudi Arabia to coordinate U.S. military and intelligence support." U.S. CENTCOM personnel were deployed to provide related support, and U.S. mid-air refueling of coalition aircraft began in April 2015 and ended in November 2018.34

In the years since, the Saudi military and its coalition partners have provided advice and military support to a range of pro-Hadi forces inside Yemen, while waging a persistent air campaign against the Houthis and their allies. Saudi ground forces and Special Forces have conducted limited cross-border operations, and Saudi naval forces limit the entry and exit of vessels from Yemen's ports. Separately, a United Nations Verification and Inspection Mechanism (UNVIM) has operated since May 2016 to assist in validating commercial sea and air traffic in support of the arms embargo imposed by Resolution 2216.

According to President Trump's December 2018 letter to Congress consistent with the War Powers Resolution, U.S. Armed Forces, "in a non-combat role,"

continued to provide military advice and limited information, logistics, and other support to regional forces combatting the Houthi insurgency in Yemen; however, aerial refueling of regional forces' aircraft ended in November 2018. United States forces are present in Saudi Arabia for this purpose. Such support does not involve United States Armed Forces in hostilities with the Houthis for the purposes of the War Powers Resolution.35

U.S. Counterterrorism Operations in Yemen

As the Saudi-led coalition's campaign against the Houthis continues and Yemen fragments, the United States has sustained counterterrorism operations against Al Qaeda in the Arabian Peninsula (AQAP) and various affiliates of the Islamic State. In total, CENTCOM conducted 36 air strikes in Yemen in 2018.36 According to President Trump's December 2018 letter to Congress consistent with the War Powers Resolution, "a small number of United States military personnel are deployed to Yemen to conduct operations against al-Qa'ida in the Arabian Peninsula (AQAP) and ISIS‑Yemen."37 In December 2018, General Frank McKenzie testified before the Senate Armed Services Committee stating that "they [AQAP] have an aspiration to attack the United States. They are prevented from generating that only because of the direct pressure that remains on them. So that is a clear, unequivocal national interest of the United States."38

Some observers contend that AQAP's power inside Yemen has diminished considerably as a result of losses sustained from U.S. counterterrorism operations and of competing Yemeni factions vying for supremacy. According to Gregory D. Johnsen, resident scholar at the Arabia Foundation, "AQAP is weaker now than it has been at any point since it was formed in 2009."39

In August 2018, U.S. officials claimed that one of the most high-value targets in the AQAP organization, bomb maker Ibrahim al Asiri, had been killed in a U.S. air strike last year. Asiri was a Saudi national who was believed to have created the explosive devices used in the 2009 Christmas Day attempted bombing of Northwest Airlines Flight 253, in a 2009 attack against former Saudi Arabian intelligence chief Mohammed bin Nayef, and in the October 2010 air cargo packages destined for Jewish sites in Chicago.

In January 2019, U.S. officials confirmed that Jamal al-Badawi, an al Qaeda operative involved in the October 2000 bombing of the USS Cole in Aden, was killed in a precision strike in Marib governorate on January 1. Al-Badawi had been indicted by a federal grand jury in 2003 for the murder of U.S. nationals and U.S. military personnel.40

To date, two American soldiers have died in the ongoing U.S. counterterrorism campaign against AQAP and other terrorists inside Yemen. In January 2017, Ryan Owens, a Navy SEAL, died during a counterterrorism raid in which between 4 and 12 Yemeni civilians also were killed, including several children, one of whom was a U.S. citizen. The raid was the Trump Administration's first acknowledged counterterror operation. In August 2017, Emil Rivera-Lopez, a member of the elite 160th Special Operation Aviation Regiment, died when his Black Hawk helicopter crashed off the coast of Yemen during a training exercise.

Yemen's Humanitarian Crisis

Humanitarian Conditions and Assistance

According to the United Nations, Yemen's humanitarian crisis is the worst in the world, with close to 80% of Yemen's population of nearly 30 million needing some form of assistance.41 The U.N.Office for the Coordination of Humanitarian Affairs (OCHA) estimates that two-thirds of the population is food insecure, one-third are suffering from extreme levels of hunger, and 230 out of Yemen's 333 districts were at risk of famine as of January 2019.42 In sum, the United Nations notes that humanitarian assistance is "increasingly becoming the only lifeline for millions of Yemenis."43

As noted above, on February 17, the parties to the conflict began to implement the Stockholm Agreement. The deal calls for main roads to reopen from Hudaydah to Sanaa and Taiz and humanitarian access to the Red Sea Mills grain storage facility, which holds enough grain to provide food for 3.7 million Yemenis for a month. Access to the Mills has been cut off since September 2018.

On February 26 in Geneva, the United Nations and the Governments of Sweden and Switzerland hosted the third annual pledging conference for the crisis in Yemen. Saudi Arabia and the UAE each pledged $750 million.44 For 2019, the United Nations is seeking $4 billion from donors for programs in Yemen. The 2018 humanitarian appeal sought a little over $3 billion, of which donors have provided $2.58 billion to date.45 The United States, Saudi Arabia, the United Arab Emirates, and Kuwait combined accounted for 66.8% of all contributions to the 2018 appeal.46

Between FY2018 and FY2019, the United States has provided $720.8 million in emergency humanitarian aid for Yemen.47 Most of these funds ($498 million) are provided through USAID's Office of Food for Peace to support the World Food Programme in Yemen. Since March 2015, the United States has been the largest contributor of humanitarian aid to Yemen, with more than $1.71 billion in U.S. funding provided since FY2015. The United States provided a total of $566.2 million in humanitarian assistance in FY2018. Funds were provided to international aid organizations from USAID's Office of Foreign Disaster Assistance (OFDA), USAID's Food for Peace (FFP), and the U.S. Department of State's Bureau of Population, Refugees, and Migration (State/PRM).

Humanitarian conditions continue to be undermined both by economic disruptions caused by the fracturing of the country's financial system and by access constraints imposed by parties to the conflict.

Table 2. U.S. Humanitarian Response to the Complex Crisis in Yemen:

(in millions of dollars)
















MRA (State/PRM)










Source: Yemen, Complex Emergency—USAID Factsheets.

Food Insecurity and the Depreciation of Yemen's Currency

Remote regions of northern Yemen deep in Houthi territory are often the most challenging areas in which to deliver food aid. In most other parts of the country, food is available for purchase in the marketplace but prices are unaffordable for wide swaths of the population. According to the Food and Agriculture Organization of the United Nations, "The average cost of the minimum survival food basket—comprised of the minimum items required for a household to survive for one month—remains more than 110 percent higher than prior to the conflict's escalation in March 2015."48

One cause of inflationary prices is the depreciation of the national currency (rial). Yemen has two competing central banks, one in Sanaa (run by the Houthis) and one in Aden (run by the Hadi government). The Houthis in Sanaa have depleted the original central bank's foreign currency reserves and have been unable to pay public sector salaries. The central bank in Aden has liberally printed money, which has driven down the value of the rial.49 According to the Economist Intelligence Unit's outlook for 2019, "rapid currency depreciation for most of 2018 significantly increased the price of imports [most Yemeni food is imported], and, despite a rally in the rial in late 2018, is a trend that is likely to continue throughout the forecast period as the Aden-based authorities continue to print money..."50 In 2018, Saudi Arabia agreed to lend $2 billion with the central bank in Aden to help the Hadi government finance food imports. However, according to one report, as of November 2018, "only a little over $170 million had been authorized for payment."51

Restrictions on the Flow of Commercial Goods and Humanitarian Aid

One of the key aspects of the 2015 United Nations Security Council Resolution (UNSCR) 2216 is that it authorizes member states to prevent the transfer or sale of arms to the Houthis and also allows Yemen's neighbors to inspect cargo suspected of carrying arms to Houthi fighters. In March 2015, the Saudi-led coalition imposed a naval and aerial blockade on Yemen, and ships seeking entry to Yemeni ports required coalition inspection, leading to delays in the off-loading of goods and increased insurance and related shipping costs. Since Yemen relies on foreign imports for as much as 90% of its food supply, disruptions to the importation of food exacerbate already strained humanitarian conditions resulting from war.

To expedite the importation of goods while adhering to the arms embargo, the European Union, Netherlands, New Zealand, the United Kingdom, and the United States formed the U.N. Verification and Inspection Mechanism (UNVIM), a U.N.-led operation designed to inspect incoming sea cargo to Yemen for illicit weapons. UNVIM, which began operating in February 2016, can inspect cargo while also ensuring that humanitarian aid is delivered in a timely manner.

However, Saudi officials argue that coalition-imposed restrictions and strict inspections of goods and vessels bound for Yemen are still required because of Iranian weapons smuggling to Houthi forces. Saudi officials similarly argue that the delivery of goods to ports and territory under Houthi control creates opportunities for Houthi forces to redirect or otherwise exploit shipments for their material or financial benefit.52

According to the latest reporting from United Nations Office for the Coordination of Humanitarian Affairs (U.N.OCHA), over the last several months, the volume of cargo discharged at Hudaydah and Saleef ports dropped, and now is 20% less than when the conflict began in 2015.53

Water, Sanitation, and Hygiene (WASH)

Yemen is experiencing the world's largest ongoing cholera outbreak. Since late 2016, there have been more than 1.3 million suspected cholera cases and nearly 2,800 associated deaths.54 Cholera is a diarrheal infection that is contracted by ingesting food or water contaminated with the bacterium Vibrio cholerae. Yemen's water and sanitation infrastructure have been devastated by the war. Basic municipal services such as garbage collection have deteriorated and, as a result, waste has gone uncollected in many areas, polluting water supplies and contributing to the cholera outbreak. In addition, international human rights organizations have accused the Saudi-led coalition of conducting air strikes that have unlawfully targeted civilian infrastructure, such as water wells, bottling facilities, health facilities, and water treatment plants.

Humanitarian organizations working in the WASH sector have improved cholera prevention and reduced the frequency of new cases, but have not eliminated the crisis. According to U.N.OCHA's 2019 Yemen Humanitarian Needs Overview, "Public water and sanitation systems require increased support to provide minimum services and avoid collapse. Some 22 per cent of rural and 46 per cent of urban populations are connected to partially functioning public water networks, and lack of electricity or public revenue creates significant reliance on humanitarian support."55 As of January 2019, 17.8 million people in Yemen are living without access to safe water and sanitation, and 19.7 million lack access to adequate health care.

Where is the Yemen Conflict Heading?

While the Stockholm Agreement has the potential to lead to a broader, nation-wide cease-fire, the longer it takes to implement, the greater risk of the agreement's collapse and the prospect for renewed conflict in Hudaydah. Although fighting has continued along several fronts since December 2018, the Stockholm Agreement has provided the Saudi-led coalition with the possibility of gradually extricating itself its intervention in Yemen. If the cease-fire collapses, then the coalition would have to weigh the benefits of trying to evict the Houthis from Hudaydah militarily with the humanitarian costs to the Yemeni people and the reputational damage it would incur within the international community.

Even if the United Nations is able to make progress toward a comprehensive peace agreement, Yemen is still beset by multiple political conflicts and violence. In the south, regional secessionists are at odds with what remains of President Hadi's internationally recognized government. In the partially Houthi-besieged city of Taiz, Yemen's third-largest city, rival militias backed by the coalition have engaged in internecine warfare56 and have been accused by human rights groups of committing war crimes.57

Many key questions about the future of Yemen remain unanswered. In the context of the current Houthi-Saudi-led coalition conflict, few observers have insight into whether or under what conditions the Houthis might be willing to relinquish their heavy or advanced weaponry used to threaten Saudi Arabia, the United Arab Emirates, and maritime shipping. Iran, now involved in Yemen in new ways, may prove unwilling to sever ties that vex its Saudi adversaries. Political and military compromise between the coalition and the Houthis could bring fighting to an end, but might also entrench an anti-U.S. and anti-Saudi Houthi movement as a leading force in a new order in Yemen.

The complexity of Yemen's internal politics and the short-term need to resolve the current conflict have overshadowed domestic and international consideration of what the future of Yemeni governance may be. Overall, the prospects for returning to a unified Yemen appear dim. According to the United Nations Panel of Experts on Yemen, "The authority of the legitimate Government of Yemen has now eroded to the point that it is doubtful whether it will ever be able to reunite Yemen as a single country." While the country's unity is a relatively recent historical phenomenon (dating to 1990), the international community had widely supported the reform of Yemen's political system under a unified government just a few years ago. In 2013, Yemenis from across the political spectrum convened a National Dialogue Conference aimed at reaching broad national consensus on a new political order. However, in January 2014 it ended without agreement, and the Houthis launched a war.

The failure of the 2013 National Dialogue Conference aimed at reaching broad national consensus on a new political order continues to violently reverberate throughout Yemen. If some semblance of normalcy is to return to the country, local players will have to return to addressing key issues, such as the power of a central government, the devolution of power to regional authorities, and the composition of national security forces. The longer these issues remain unresolved, the greater the prospect for Yemen's dissolution into competing self-declared autonomous regions.

Author Contact Information

Jeremy M. Sharp, Specialist in Middle Eastern Affairs ([email address scrubbed], [phone number scrubbed])



USAID, Food Assistance Fact Sheet Yemen, updated January 31, 2019.


"Press Release: Yemen War Death Toll now Exceeds 60,000 according to latest ACLED Data," The Armed Conflict Location & Event Data Project (ACLED), December 11, 2018. Save the Children reports that an additional 85,000 children under the age of five may have died of starvation and disease, based on an analysis of UNICEF/Nutrition Cluster data malnutrition estimates between 2015 and 2018. See:


"UNHCR Operational Update: Yemen," UNHCR, January 11 2019.


Letter dated 25 January 2019 from the Panel of Experts on Yemen addressed to the President of the Security Council, S/2019/83, United Nations Security Council.


The full text of the cease-fire agreements are available at: [].


After a month, the U.N.-appointed RCC chair, retired Dutch general Patrick Cammaert, announced that he would be stepping down and would be replaced by Danish Major General Michael Anker Lollesgaard, who led a U.N. peacekeeping mission in Mali in 2015 and 2016.


"U.N. Envoy urges Yemen Combatants to withdraw from Lifeline Port," Reuters, January 28, 2019.


"Explainer: What's so Hard about Implementing a Peace Deal in Yemen's Main Port," Reuters, February 26, 2019.


"Yemen's Parties agree to start stalled troop withdrawal from Main Port, Reuters, February 17, 2019.


International Crisis Group, Yemen Update #1, Briefing Note / Middle East & North Africa 24 January 2019.


Office of the Special Envoy of the Secretary General for Yemen, Statement by The Special Envoy of the Secretary General for Yemen, Martin Griffiths, On The Implementation of the Hudayda Agreement, March 19, 2019.


"Yemen: Consultations on the Hodeidah Agreement," What's In Blue, March 12, 2019.


"Making Yemen's Hodeida Deal Stick," International Crisis Group, December 19, 2018.


"Yemen: Consultations on Implementation of Resolutions," What's in Blue, January 30, 2019.


In winter 2019, UAE forces and UAE-supported Yemeni units helped rescue Danny Lavone Burch, a U.S. citizen who had been kidnapped and held for ransom by a Yemeni criminal gang for nearly 18 months. See, "Arab Raid Led to Freedom for American Hostage in Yemen," New York Times, March 6, 2019.


For an overview of the role of Congress in the Yemen conflict, see CRS Report R45046, Congress and the War in Yemen: Oversight and Legislation 2015-2019. See, Murphy, Durbin, Lee Lead 20 Senators in Pressing State Department & DOJ for Information on Saudi-Led War In Yemen, January 23, 2019.


Senate Foreign Relations Committee Holds Hearing on Pending Nominations, CQ Congressional Transcripts Congressional Hearings, Dec. 4, 2018.


U.S. Central Command, Senate Armed Services Committee, Testimony: Joseph Votel, USA, Commander, U.S. Central Command, February 5, 2019.


"Saudi-led Coalition denies Unauthorised Weapons transfers to Yemeni Forces," Jane's Defence Weekly, February 11, 2019.


U.S. State Department, Yemen Quad Meeting in Warsaw, State Department Press Releases And Documents, February 14, 2019,


The White House, Statement of Administration Policy, H.J.Res. 37 – Directing the President to Remove United States Armed Forces from Hostilities in the Republic of Yemen that Have Not Been Authorized by Congress, February 11, 2019.


According to the U.S. intelligence community, "Iran's support to the Houthis further escalates the conflict and poses a serious threat to US partners and interests in the region. Iran continues to provide support that enables Houthi attacks against shipping near the Bab al Mandeb Strait and land-based targets deep inside Saudi Arabia and the UAE." See Office of the Director for National Intelligence, Testimony Prepared for Hearings on Worldwide Threats, February 2018.


For example, see the following: "Report: Bombs disguised as Rocks in Yemen show Iranian Aid," Associated Press, March 26, 2018; "Iran Steps up Support for Houthis in Yemen's War – Sources," Reuters, March 21, 2017; "Maritime Interdictions of Weapon Supplies to Somalia and Yemen: Deciphering a Link to Iran," Conflict Armament Research, November 2016; "U.S. Officials: Iran Supplying Weapons to Yemen's Houthi Rebels," NBC News, October 27, 2016; "Exclusive: Iran steps up Weapons Supply to Yemen's Houthis via Oman—Officials," Reuters, October 20, 2016; "Weapons Bound for Yemen Seized on Iran Boat: Coalition," Reuters, September 30, 2015; and "Elite Iranian guards training Yemen's Houthis: U.S. officials," Reuters, March 27, 2015.


"The Houthi Hezbollah: Iran's Train-and-Equip Program in Sanaa," Foreign Affairs, March 31, 2016.


U.S. Mission to the United Nations, Press Release: "Ambassador Haley on Weapons of Iranian Origin Used in Attack on Saudi Arabia," November 7, 2017.


"Letter dated 26 January 2018 from the Panel of Experts on Yemen mandated by Security Council resolution 2342 (2017) addressed to the President of the Security Council," United Nations Panel of Experts on Yemen, S/2018/68, January 26, 2018.


"U.N.panel finds further Evidence of Iran Link to Yemen Missiles,"Agence France Presse, July 30, 2018.


U.S. Department of the Treasury, Treasury Targets Iranian Individuals Providing Ballistic Missile Support to Yemen's Huthis, May 22, 2018.


U.S. Congress, Senate Select Committee on Intelligence, Statement for the Record: Worldwide Threat Assessment of the US Intelligence Community, 116th Cong., 1st sess., January 29, 2019.


Letter dated 25 January 2019 from the Panel of Experts on Yemen addressed to the President of the Security Council, S/2019/83, United Nations Security Council.


Bruce Riedel, "Who are the Houthis, and Why are we at War with them?" Brookings, MARKAZ, December 18, 2017.


During the Cold War, Saudi Arabia's leaders supported northern Yemeni Zaydis as a bulwark against nationalist and leftist rivals, and engaged in proxy war against Egypt-backed Yemeni nationalists during the 1960s. The revolutionary, anti-Saudi ideology of the Houthi movement, which emerged in the 1990s, presented new challenges. In 2009, Saudi Arabia launched a three month air and ground campaign in support of the Yemeni government's Operation Scorched Earth. Saudi Arabia dispatched troops along the border of its southernmost province of Jizan and Sa'dah in an attempt to repel reported Houthi infiltration of Saudi territory. It is estimated that Saudi Arabia lost 133 soldiers in its war against the Houthis. Saudi Arabia agreed to a ceasefire with the Houthis in late February 2010 after an exchange of prisoners and remains.


President Hadi correspondence with GCC governments printed in U.N. Document S/2015/217, "Identical letters dated 26 March 2015 from the Permanent Representative of Qatar to the United Nations addressed to the Secretary-General and the President of Security Council," March 27, 2015.


Refueling operations began April 7, 2015 according to Department of Defense spokesman Col. Steve Warren. See Andrew Tilghman, "U.S. launches aerial refueling mission in Yemen," Military Times, April 8, 2015.


Letter from the President to the Speaker of the House of Representatives and the President Pro Tempore of the Senate, December 7, 2018.


U.S. Central Command, "CENTCOM Counterterrorism Strikes In Yemen 2019 Rollup," press release, January 7, 2019.


Letter from the President to the Speaker of the House of Representatives and the President Pro Tempore of the Senate, December 7, 2018.


Senate Armed Services Committee Holds Hearing on Pending Nominations, CQ Congressional Transcripts, December 4, 2018.


"Al-Qaeda and ISIS are on Their Heels in Yemen, But Will Return Unless We Help Build a Lasting Peace," Just Security, August 7, 2018.


U.S. Central Command, "USCENTCOM Confirms the Death of Jamal al-Badawi," press release, January 7, 2019.


"Humanitarian Crisis in Yemen Remains the Worst in the World, Warns UN," UN News, February 14, 2019.


"Yemen Humanitarian Update Covering January 16-23," U.N.Office for the Coordination of Humanitarian Affairs, January 23, 2019, Issue 2.


"Yemen: 2019 Humanitarian Needs Overview," U.N.Office for the Coordination of Humanitarian Affairs, U.N.Country Team in Yemen, February 14, 2019.


United Nations, High-Level Pledging Event for the Humanitarian Crisis in Yemen, Geneva, Switzerland, February 26, 2019.


"Secretary-General's remarks to the Pledging Conference for Yemen [as delivered]," United Nations Secretary-General, February 28, 2019.


"Yemen 2018 (Humanitarian Response Plan)," Financial Tracking Service.


USAID, Yemen - Complex Emergency Fact Sheet #5, FISCAL YEAR (FY) 2019 February 26, 2019.


op. cit.


"In Yemen, an Unnatural Disaster," Washington Post, December 30, 2018.


Economist Intelligence Unit, Country Report Yemen, February 19, 2019.


"A Bank Divided: Yemen's Financial Crisis Hits Food Imports," Reuters, December 20, 2018.


Saudi Press Agency, Command of the Coalition to Restore Legitimacy in Yemen Issues Statement, November 22, 2017.


"Yemen Humanitarian Update Covering January 16-23," U.N. Office for the Coordination of Humanitarian Affairs, January 23, 2019, Issue 2.


"Weekly Epidemiological Monitor," World Health Organization, Vol. 11, No. 52, December 30, 2018.


"Yemen: 2019 Humanitarian Needs Overview," U.N. Office for the Coordination of Humanitarian Affairs, February 14, 2019.


"In Ancient Yemeni City, Violence turns Inward," Washington Post, December 6, 2018.


"Yemen: Ta'iz Authorities must tackle Child Rape and Abuse under Militia Rule," Amnesty International, March 8, 2019.