Yemen: Civil War and Regional Intervention

Updated September 17, 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 civilians as well as combatants, and has significantly damaged the country's infrastructure. One U.S.- and European-funded organization, the Armed Conflict Location & Event Data Project (ACLED), estimated in June 2019 that more than 90,000 Yemenis have been killed since 2015, including more than 30,000 in 2018 and nearly 12,000 in 2019.

Despite multiple attempts by the United Nations (U.N.) to broker a cease-fire that would lead to a comprehensive settlement to the conflict, the parties themselves continue to hinder diplomatic progress. In December 2018, the Special Envoy of the U.N. Secretary-General for Yemen Martin Griffiths brokered a cease-fire, known as the Stockholm Agreement, centered on the besieged Red Sea port city of Hudaydah. Eight months later, the agreement remains unfulfilled and, though fighting around Hudaydah has subsided, other fronts have intensified. Parallel initiatives to secure the western city of Taiz and exchange prisoners also remain to be implemented.

Although media coverage of the 2015 Saudi-led intervention tended to focus on the binary nature of the war (the Saudi-led coalition versus the Houthis), in fact, there have been a multitude of combatants whose alliances and loyalties have been somewhat fluid. In the summer of 2019 in southern Yemen, long simmering tensions between the internationally recognized Republic of Yemen government (ROYG) and the separatist Southern Transitional Council (STC) boiled over, leading to open warfare between the local allies of Saudi Arabia and the United Arab Emirates.

Many foreign observers have denounced human rights violations that they charge have been committed by all parties to the conflict. In the United States and other Western countries, there has been vociferous opposition to errant coalition air strikes against civilian targets. Some lawmakers have proposed legislation to limit U.S. support for the coalition while others have highlighted Iran's support for the Houthis as a major factor in Yemen's destabilization. The Trump Administration opposes congressional efforts to restrain U.S. support for Saudi Arabia and continues to call for a comprehensive settlement to the conflict in line with relevant U.N. Security Council resolutions and other international initiatives.

According to U.N. officials, 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. The United Nations notes that humanitarian assistance is "increasingly becoming the only lifeline for millions of Yemenis." As of mid-September 2019, U.N. financial appeals for 2019 programming in Yemen sought $4.2 billion, but had received only $1.5 billion (36%) through U.N. plan channels.

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.

Historical Background and Overview

For over a decade, the Republic of Yemen Government (ROYG) has been torn apart by multiple armed conflicts to which several internal militant groups and foreign nations are parties. Collectively, these conflicts have eroded central governance in Yemen, and have fragmented the nation into various local centers of power. Though until 1990, Yemen was largely devoid of a single government, the gradual dissolution of Yemen's territorial integrity has alarmed the international community and the United States. Policymakers are concerned that state failure may empower Yemen-based transnational terrorist groups; destabilize vital international shipping lanes near the Bab al Mandab strait (alt. sp. Bab al Mandeb, Bab el Mendeb); and provide opportunities for Iran to threaten Saudi Arabia's borders. Beyond geo-strategic concerns, the collapse of Yemeni institutions during wartime has exacerbated poor living conditions in what has long been the most impoverished Arab country, leading to what is now considered the world's worst humanitarian crisis.

Table 1. Key Groups in Yemen Conflict


Republic of Yemen Government (ROYG)
The internationally recognized government has been led by Abdu Rabbu Mansour Hadi since 2012, when he was elected as caretaker president to replace President Ali Abdullah Saleh, who had been in power for 33 years. The Hadi government has been backed by the Saudi-led coalition since 2015.


Houthi Forces
The Houthi movement (also known as Ansar Allah or Partisans of God) is a predominantly Zaydi Shiite revivalist political and insurgent movement formed in the northern Yemeni governorate of Sa'dah under the leadership of members of the Houthi family. The group was allied with former President Ali Abdullah Saleh until 2017.


Al Qaeda in the Arabian Peninsula (AQAP)
AQAP has operated in Yemen since 2009 as a successor to previously active AQ members in the country, and since has been most active in Yemen's southern governorates. AQAP enjoys support from some inland tribes and has taken and held territory along Yemen's southern coast with varying degrees of success since 2015. AQAP has attempted to carry out attacks in the United States and Europe.


Southern Transitional Council (STC)
A southern separatist force backed by the United Arab Emirates since the spring of 2017, the STC is led by Yemeni General Aidarous al Zubaidi, former governor of Aden. The STC and Hadi government have been at odds over the inclusion of Yemen's main Sunni Islamist party (Al Islah) in Hadi's government. In August 2019, the STC took control of Aden, Yemen's interim capital.

For nearly five years, one conflict in particular has garnered the bulk of international attention – the intervention of Saudi Arabia's international coalition against the northern Yemeni-based Ansar Allah/Houthi movement (referred to in this report as "the Houthis"). In 2014, Houthi militants took over the capital, Sanaa (also commonly spelled Sana'a), and in early 2015, advanced southward from the capital 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 (referred to in this report as "the Saudi-led coalition") launched a military offensive aimed at restoring Hadi's rule and evicting Houthi fighters from the capital and other major cities.1

Now in its fifth year, the war in Yemen shows no signs of abating. The war has killed tens of thousands of Yemenis, including civilians as well as combatants, and has significantly damaged the country's infrastructure. One U.S. - and European-funded organization, the Armed Conflict Location & Event Data Project (ACLED), estimated in June 2019 that more than 90,000 Yemenis have been killed since 2015.2

Despite multiple attempts by the United Nations to broker a cease-fire that would lead to a comprehensive settlement to the conflict, the parties themselves continue to hinder diplomatic progress. In December 2018, the Special Envoy of the United Nations Secretary-General for Yemen Martin Griffiths brokered a cease-fire, known as the Stockholm Agreement, centered on the besieged Red Sea port city of Hudaydah (alt. sp. Hodeidah, Al Hudaydah). Eight months later, the agreement remains unfulfilled and, though fighting around Hudaydah has subsided, other fronts have intensified.

Although media coverage since the 2015 Saudi-led intervention has tended to focus on the binary nature of the war (the Saudi-led coalition versus the Houthis), in fact, there have been a multitude of combatants whose alliances and loyalties have been somewhat fluid. In the summer of 2019 in southern Yemen, long simmering tensions between the ROYG and the Southern Transitional Council (STC), a southern Yemeni separatist group backed by the United Arab Emirates (UAE), boiled over, leading to open warfare between the local allies of Saudi Arabia and the United Arab Emirates.

Many foreign observers have denounced human rights violations that they charge have been committed by all parties to the conflict, with particular attention paid in the United States and other Western countries to errant coalition air strikes against civilian targets. Some lawmakers have proposed legislation to limit U.S. support for the coalition, while others have highlighted Iran's support for the Houthis as a major factor in Yemen's destabilization. The Trump Administration continues to call for a comprehensive settlement to the conflict in line with in line with relevant resolutions of the United Nations Security Council and other international initiatives.

The Houthi-Saudi War

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 non-state, non-Sunni actor who can pressure Iran's adversaries both politically and militarily (akin to Hezbollah in Lebanon).3 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 2004.4 The Houthis rejected what they viewed as hostile, Saudi-supported proselytization efforts in northern Yemen.5

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, son of Ali (the cousin and son-in-law of the prophet Muhammad). 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 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 C.E. 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, it is doctrinally distinct from "Twelver Shiism," the dominant branch of Shia Islam in Iran and Lebanon. Zaydism's legal traditions and religious practices are more similar to Sunni Islam.

The Houthi movement was formed in the northern Yemeni governorate 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 Saudi-backed 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!"

From the outset of the Saudi-led coalition intervention, 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 amid intense congressional scrutiny in November 2018.6

Since 2015, the Saudi military and its coalition partners have waged a persistent air campaign against the Houthis and their allies. This air campaign has at times drawn international criticism for growing civilian casualties from coalition air strikes. Most recently, on September 1, 2019, the Saudi-led coalition conducted air strikes against a Houthi-run detention center, killing over 100 people. The coalition claims that it struck a legitimate military target, which was both a prison and a storage site for Houthi unmanned aerial vehicles (UAVs). 7 Human rights activists assert that the International Committee for the Red Cross had visited the site, and it was well known as a Houthi-run prison.8 According to a recent U.N Human Rights Council Report on Yemen, which found human rights violations on all sides of the conflict between 2018 and 2019, despite "reported reductions in the overall number of airstrikes and resulting civilian casualties, the patterns of harm caused by airstrikes remained consistent and significant."9

Figure 1. Lines of Control in Yemen

As of September 2019

Source: Graphic created by CRS using data from Risk Intelligence (2019); Esri (2017 & 2018); NOAA (2018); USGS (2018); Department of State (2015).

During the spring and summer of 2019, as U.S.-Iranian tensions escalated in the Gulf, the Houthis and their transnational supporters markedly increased their drone and missile attacks against Saudi Arabia's energy and water infrastructure and commercial airports. In May 2019, several days after Saudi Aramco pumping stations were targeted inside the kingdom, the Houthis announced that this attack marked the beginning of a wider campaign aimed at 300 "vital military targets" inside Saudi Arabia, the UAE, and their bases in Yemen.10 A month later, the Houthis also announced that they would conduct an "airport for airport" campaign, asserting that so long as the Saudi-led coalition maintains its three-year closure of Sanaa airport, the Houthis will target Saudi civilian airports.

Since June, the Houthis have launched multiple UAV and missile attacks against regional airports in Saudi Arabia (Jizan, Najran, and Abha), forcing the suspension of flights, damaging runways, and killing several civilians. Iran is believed to be the original source of some UAV and missile technology and related knowledge transfers to the Houthis.11 However, the Houthis also may now be manufacturing their own UAVs and missiles. According to Jane's Defence, "the available evidence suggests that Ansar Allah is increasingly making use of parts that are commercially available on the international market to develop new UAV designs."12

Figure 2. The Houthi Displayed "Sammad-3 long-range UAV"

Source: Jane's Defence Weekly.

Overall, after five years of military operations against the Yemeni government and Saudi-led coalition, it would appear that the Houthis are better equipped with sophisticated weaponry than in previous conflicts against its rivals. According to one observer, "We have witnessed a massive increase in capability on the side of the Houthis in recent years, particularly relating to ballistic missiles and drone technology…. The current capability is far more advanced than anything the Yemeni armed forces had before the civil war."13 In July 2019, the Houthis publicly displayed cruise missiles and UAVs in their arsenal and, according to one analysis, the Houthis are "revealing capabilities that Iran has been developing secretly for years."14

On September 14, 2019, drone and missile attacks against two key Saudi oil sites deep inside the kingdom led to a dramatic escalation in the ongoing conflict. The attacks against Saudi Arabia's Abqaiq refinery plant and the Khurais oil field temporarily disrupted an estimated 5.7 million barrels of crude oil production per day, equivalent to more than 5% of the world's daily supply. The Houthis claimed responsibility for the attack, boasting that they had exploited "vulnerabilities" in Saudi Arabia's air defenses. However, the Trump Administration initially implied that the attacks against the facilities may have originated from Iran rather than northern Yemen. In addition, due to the large number of projectiles used in carrying out the coordinated attack, there has been some speculation that the Houthis, despite their growing capabilities, lacked the capabilities to carry out such a precise military operation.15

The Situation in South Yemen


Southern Yemen refers to a vast geographic area roughly conforming to the boundaries of the former socialist independent republic known as the People's Democratic Republic of Yemen (PDRY), which lasted from 1967 to 1990. The political and geographic landscape of southern Yemen is markedly different from the north; whereas the northern highlands of Yemen had been ruled for centuries as a religious monarchy by various Zaydi Imams, the southern interior was less centrally controlled and divided into smaller political entities and tribal territories. Yemen's second largest city of Aden has served as the south's main urban area. Its political culture has been influenced by a history of both British colonial and post-colonial socialist rule.16 Over the last few decades, terrorist groups, such as Al Qaeda in the Arabian Peninsula (AQAP), have taken root in several southern governorates, finding safe haven amongst certain tribes.

For most of its 23-year existence, the PDRY was dependent on foreign sponsors such as the Soviet Union; when the Soviet Union collapsed, southern leaders turned to the north and the idea of unification. However, since Yemen's unity in 1990, southern Yemenis have been disaffected because of their perceived second-class status in a unified state. Many of their leaders tried to secede during a civil war in 1994. Civil unrest in Yemen's southern governorates reemerged in 2007, when civil servants and military officers from the former PDRY began protesting low salaries and the lack of promised pensions. Those disaffected southerners started a broader protest movement, known as the Southern Mobility Movement (SMM or, in Arabic, Al Harakat al Janubi or Hirak), which itself was divided between secessionist and federalist branches.

After popular uprisings swept across the Arab world in 2011, including in Yemen, the Gulf Cooperation Council (GCC) helped broker a transition plan for Yemen.17 As part of Yemen's transition from the longtime rule of President Ali Abdullah Saleh (ruled unified Yemen from 1990-2012) to President Hadi, all of Yemen's various political factions (565 individual delegates) held what was called the National Dialogue Conference (NDC) from 2013-2014. That conference was intended to settle all of Yemen's outstanding political issues, including addressing southern calls for greater autonomy. However, many younger southern activists decried the NDC, arguing that southern representatives who attended the NDC were out of touch with the demands of a new generation and therefore lacked legitimacy, particularly after many southern delegates were appointed by President Hadi.18 After the NDC concluded, a Hadi-appointed committee then proposed to divide Yemen into six federal regions, four of which would be in the north and two in the south – a proposal that was immediately rejected by southern leaders (as well as by the Houthis in the north).

In 2015, when the Saudi-led coalition evicted the Houthis from Aden and its environs, Aden became the Hadi-led ROYG's de-facto capital. In reality, the ROYG's physical presence in Aden was minimal and relegated to a presidential palace, the Central Bank, and few other buildings. The rest of the city was plagued by insecurity and, over time, the UAE and its southern separatist allies emerged as primary power brokers in Aden.19

UAE reasoning for building a political base in southern Yemen is multifaceted. UAE involvement in the Saudi-led coalition has allowed the Emirates to cooperate more openly with the United States in countering terrorist groups, such as AQAP in southern Yemen.20 It also has allowed Emirati forces to exercise influence in various Yemeni port cities that could compliment UAE commercial and energy interests in the Red Sea and the Gulf of Aden.

Finally, the UAE also seeks to thwart the rise of Islamist political groups, such as the Muslim Brotherhood, particularly after popular protests in 2011 empowered some of these movements across the region. In Yemen, the tribal/Sunni Islamist movement known as Al Islah (Reform) has been a major player in national politics for decades and, since the Houthi offensive in 2014, it aligned itself with the ROYG and Saudi Arabia. In order to counter the ROYG-Saudi-Islah alliance, the UAE chose to align itself with southern separatists. In the spring of 2017, the UAE supported Yemeni General Aidarous al Zubaidi's formation of the Southern Transitional Council (STC) after Hadi dismissed him as Aden's governor.

From 2015 to 2019, the UAE exerted influence in Aden through the presence of its own troops or STC-allied tribal militia (known as the Southern Belt/Security Belt or Al Hizam al Amni in Arabic). President Hadi's only personally loyal military force in Aden had been the Presidential Protection Force (commanded by his son Nasser), which was relatively small compared to UAE-allied forces.21 Periodic clashes between ROYG forces and UAE-backed forces occurred and, in January 2018, the STC seized control of most of Aden from ROYG troops in just three days. The UAE and Saudi Arabia intervened in order to ensure that the STC would remain committed to the larger fight against the Houthis. After the fighting subsided, the STC declared that it would continue to participate in the coalition's military operations against the Houthis and handed back military installations to ROYG forces. Nevertheless, at the time, it appeared that Hadi had an Aden-based government in name only and that, on the ground, power resided in the hands of the STC.

STC-ROYG Conflict

In the summer of 2019, fighting dramatically escalated between STC and ROYG-aligned forces, ultimately leading to the ROYG's expulsion from Aden at the hands of the STC.

In late June 2019, amidst regional tensions between the United States and Iran, the UAE publicly announced that a redeployment of its armed forces in Yemen was underway and that while the Emiratis would not fully withdraw all forces from Yemen (and would continue counter-terrorism operations), a significant number of their troops would return to the UAE in case of a conflict with Iran.22 In addition to concerns regarding Iran, Emirati officials may have been concerned that the coalition's conduct of military operations in Yemen was damaging the UAE's reputation amidst a stalemated war that the coalition as constituted might lack the capability to win.23 In justifying their troop maneuvers, UAE officials emphasized that the redeployment of their forces meant that the UAE would be placing less of an emphasis on military operations and more of a push toward pursuing peace talks.24 The U.N.-brokered December 2018 Stockholm Agreement (see below), which had created a tenuous cease-fire in the port city of Hudaydah, may have been an earlier indication that the UAE had "changed its calculus" regarding the war's trajectory.25

Just a month later, on August 1, 2019, the Houthis fired missiles at a military graduation ceremony in southern Yemen, killing dozens of STC-aligned Security Belt soldiers, including Brigadier General Abu Yamamah al Yafaei, one of the top STC commanders. According to one account, General al Yafaei was a "well-known member of the al-Yafai tribe, one of the largest tribal confederations in Yemen, known for its rugged toughness and support for southern independence. Under his leadership, the Security Belt Forces recruited heavily from Yafa and surrounding areas. His stature as one of the foremost military commanders in southern Yemen made him a target for his enemies, including the Houthis and al-Qaeda."26

In the aftermath of the Houthis' missile attack, the STC blamed the Islah party for collaborating with the Houthis against them (even though the two groups are on opposite sides of the current conflict). Almost a week after the attack, fighting broke out between STC and ROYG forces inside Aden, as STC leaders called for the overthrow of the Hadi government for its alliance with Islah. After several days of fighting, the STC claimed control over Aden and had disbanded President Hadi's Presidential Protection Force.

After securing Aden, the STC continued its assault against ROYG forces in the neighboring southern governorates of Abyan and Shabwa. However, ROYG forces and allied tribal militias were able to repel the STC, due partially to emergency Saudi aid and reinforcements, forcing the STC to retreat, and several STC-allied groups switched sides to join the ranks of President Hadi. During the STC retreat, ROYG forces counter-attacked, reaching the outskirts of Aden, where reportedly the UAE launched air strikes against them in order to keep the ROYG from retaking Aden. The UAE claims that its strikes were conducted against terrorist militias that were trying to take advantage of the infighting between former coalition partners.27 Ultimately, the STC managed to retain control over Aden, though ROYG forces surprised them, showing, according to one account, "impressive defensive resilience and offensive drive."28

As of September 2019, various mediation efforts are ongoing to repair the STC-ROYG rift. One core negotiating parameter for Saudi Arabia is the recognition of ROYG legitimacy. On September 5, 2019, Saudi Arabia announced that "There is no alternative to the legitimate government in Yemen and any attempts to impose a new reality by force will not be accepted."29 Saudi Arabia has legally based its intervention in Yemen on the call by President Hadi for international assistance against the Houthis, noted in United Nations Security Council Resolution (UNSCR) 2216 (April 2015).30

It appears that the UAE and STC are working together to hold Aden for the long term, while Saudi Arabia is working with the ROYG to ensure its control over neighboring southern governorates.31 The coalition against the Houthis is now apparently divided, and Saudi Arabia and the United Arab Emirates appear to be openly working at cross-purposes. This raises questions about whether the "war within the war" in the south diminishes the likelihood of a Saudi-led coalition victory over the Houthis in the north.

Cease-Fire in Hudaydah and the Stockholm Agreement

In 2014, a month after taking control of Sanaa, Houthi militants seized Yemen's principal cargo port at Hudaydah. For the Houthis, controlling Hudaydah is vital for several reasons. Hudaydah provides the mostly land-locked northern Houthi-controlled areas with access to the Red Sea. Control of Hudaydah is key to resupplying the Houthi-controlled national capital of Sanaa. The port (Yemen's highest capacity port and second-most populous port city after Aden) is north of the Bab al Mandab strait, one of the world's maritime chokepoints.32 Hudaydah also generates revenue for the Houthis, who "tax" imports and control the distribution of food and fuel leaving the port. Hudaydah also is 25 miles south of the Ras Isa floating terminal, which, until 2015, had been used to export oil produced in the Marib oil fields via the 270-mile Marib-Ras Isa pipeline.33

Figure 3. Map of Hudaydah

Source: Middle East Eye, June 25, 2018.

Nearly four years after the Houthis' capture of Hudaydah, in June 2018, the Saudi-led coalition, spear-headed by the United Arab Emirates and its local Yemeni allies, launched Operation Golden Victory in order to change the balance of power on the ground and regain leverage in any future political settlement of the Yemen conflict. For the coalition, retaking Hudaydah was an attempt to turn the tide of the war in their favor and perhaps even facilitate their gradual disengagement from direct involvement in the conflict.

By the end of 2018, coalition forces had advanced north along the western coast all the way to Hudaydah city, where fighting there threatened to cripple port operations and thereby exacerbate Yemen's already dire humanitarian crisis. With international pressure mounting to maintain the flow of humanitarian relief through Hudaydah, Martin Griffiths, the Special Envoy of the United Nations Secretary-General for Yemen, had repeatedly tried to broker a cease-fire and stave off a final coalition assault against Hudaydah.

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. 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 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. It has since been reauthorized until January 2020.

Months after the signing of the Stockholm Agreement, implementation of it stalled. One issue was that the agreement did not specify which local actors were to assume responsibility for security in Hudaydah after both parties redeployed. On May 12, the RCC initially verified that the Houthis had handed over control of Hudaydah port to local coast guard units, though the Yemeni government disputes this finding, claiming that Houthi militiamen infiltrated the coast guard units deployed at the port.34 A month later, the RCC reported no Houthi military presence in Hudaydah since May 14, and coast guard forces were providing port security.35 In August 2019, Special Envoy Griffiths reported to the United Nations Security Council that since the signing of the Stockholm Agreement, "there have been no major military operations in Hudaydah city, or in the surrounding area, and there has been a sustained reduction in violence, as we have often observed in this Council. Aid continues to move through the ports, and this is by itself a major achievement which continues to benefit the civilian population in Hudaydah first, but also those elsewhere in Yemen who rely on that humanitarian pipeline."36 In September 2019, the RCC convened and announced that it would be deploying "monitoring teams in four locations on the frontlines of Hudaydah as an initial step aimed to sustain the ceasefire and reduce the suffering of and casualties among civilians."37

Nevertheless, the parties to the conflict have failed to fully demilitarize Hudaydah, and Houthi forces have repeatedly shelled areas near the city. Though the cease-fire is somewhat holding, without the full implementation of the Stockholm Agreement it remains tenuous. 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 parties to the conflict.38

Fighting Along Other Fronts

Over the past year, while international attention has largely focused on fighting around the port cities of Hudaydah and Aden, elsewhere in Yemen (governorates of Hajjah, Sa'dah, and Dhale), fighting between the Houthis and the Saudi-led coalition and within the coalition itself has continued. In the partially Houthi-besieged city of Taiz, Yemen's third-largest city, rival militias backed by the coalition have fought one another39 and have been accused by human rights groups of committing war crimes.40 In the spring of 2019 in Taiz, clashes broke out between armed fighters associated with the Islah party, Yemen's Sunni Islamist party nominally aligned with the Hadi government, and the Abu al Abbas brigades, a UAE-backed ultra-conservative militia. Even as Taiz continue to be shelled from the outside by Houthi forces, infighting within the city itself demonstrates ongoing power struggles between groups nominally allied against the Houthis. According to the International Crisis Group:

Yemen's war is complex and multifaceted, as Taiz demonstrates. De-escalating the conflict in the city and wider governorate requires the UN and other international players not only to reach an agreement between the Huthis and their adversaries, but also to achieve a compromise within the anti-Huthi front, namely between Islah, the Hadi government and UAE-backed groups.41

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 AQAP and various affiliates of the Islamic State. In June 2019, Saudi Arabia and ROYG troops captured the leader of the Yemeni branch of the Islamic State in the far eastern governorate of Al Mahra. Reportedly, the United States played an "advise and assist" role during the operation.42 Overall, according to President Trump's June 2019 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. The United States military continues to work closely with the Republic of Yemen Government (ROYG) and regional partner forces to dismantle and ultimately eliminate the terrorist threat posed by those groups. Since the last periodic update report, United States forces conducted a number of airstrikes against AQAP operatives and facilities in Yemen, and supported the United Arab Emirates- and ROYG-led operations to clear AQAP from Shabwah Governorate. United States Armed Forces are also prepared to conduct airstrikes against ISIS targets in Yemen.43

In 2019 in southern Yemen, AQAP has periodically struck both ROYG troops and forces allied with the STC. Fighting between the ROYG and the STC has raised some concern that a divided south will provide AQAP breathing room to reemerge as a terrorist threat both to Yemen and its neighbors.44 At the same time, terrorist groups within Yemen also have experienced their own bout of infighting, as AQAP and the Yemeni branch of the Islamic State have openly clashed both in armed exchanges and on social media. According to one expert,

ISIS tend to make much slicker media products than al-Qaeda. But in Yemen at least, al-Qaeda in the Arabian Peninsula (AQAP) is far better tuned to local populations and has been entrenched for much longer. Isis can't uproot it or replace it. Al-Qaeda's output may be earthy and primitive, but it is more authentic and less foreign than that of ISIS.45

Figure 4. U.S. Counterterrorism Strikes in Yemen

Source: Foundation for the Defense of Democracies, Long War Journal, April 2, 2019.

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 Operations Aviation Regiment, died when his Black Hawk helicopter crashed off the coast of Yemen during a training exercise.

The Humanitarian Crisis in Yemen

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.46 The U.N. Office for the Coordination of Humanitarian Affairs (OCHA) estimates that more than 20 million people are food insecure while 7.4 million people are at risk of famine. In sum, the United Nations notes that humanitarian assistance is "increasingly becoming the only lifeline for millions of Yemenis."47

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.48 For 2019, the United Nations is seeking $4.2 billion from donors for programs in Yemen, of which $1.5 billion had been received via U.N. channels as of mid-September 2019. The United States, Saudi Arabia, the United Arab Emirates, and Kuwait combined accounted for 66.8% of all contributions to the 2018 appeal.49

Since 2015, the United States has provided over $2 billion in emergency humanitarian aid for Yemen (see Table 2 below). Most of these funds are provided through USAID's Office of Food for Peace to support the World Food Programme in Yemen.

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.

One of the key aspects of the 2015 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, is intended to 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.50

U.S. Policy

Since the start of the 2015 Saudi-led intervention, Yemen's political instability has had consequences for U.S. policy that have reverberated well beyond Yemen's borders. As the Houthis have become further ensconced in northern Yemen and their military capabilities have heightened, in part due to Iranian support over the course of the ongoing conflict,51 Houthi military forces have struck targets inside Saudi territory and have periodically threatened maritime shipping in the Bab al Mandab strait. Although Iran had few institutionalized links to the Houthis before the conflict broke out in 2015, over time, reports and allegations of Iranian involvement in Yemen have become more frequent as the war has continued. In August 2019, Iran's Supreme Leader Ayatollah Ali Khamene'i hosted the Houthis in Tehran, and the Houthis formally appointed their own ambassador to Iran.52

Figure 5. Iran's Supreme Leader meets with Houthi Spokesperson

Source: Voice of America, August 14, 2019.

Yemen's instability and the Saudi and UAE intervention there also has at times strained U.S. relations with its Gulf partners. As non-governmental organizations continue to allege that certain coalition conduct of the war in Yemen amounts to human rights abuses and violations of international law,53 some lawmakers in various Western capitals, including in Washington, have not only objected to continued U.S. support for coalition military operations,54 but have called for overall reassessments of long-standing military cooperation with Gulf Arab states.55 As previously mentioned, one possible explanation for the summer 2019 phased drawdown of UAE forces from Yemen was out of concern that the reputational damage the UAE had incurred from its active participation in the war in Yemen outweighed the military results it had achieved on the ground after more than four years of warfare.

On the issue of counterterrorism, Yemen's instability has not dramatically altered U.S. policy. –Sustained, U.S.-supported counterterrorism operations have, according to various assessments, degraded terrorist groups operating in Yemen considerably.56 Nevertheless, as the Yemeni political landscape fractures further in the south, and Saudi and Emirati local allies are at odds, it is unclear how U.S. counterterrorism forces will be able to maintain effective partnerships with local actors competing for power on the ground.

In order to navigate the various issues raised by conflict in Yemen, the Trump Administration has pursued various lines of effort in its policy toward Yemen, including:

Prospects for a Political Settlement

It appears that one of the many impediments to a reaching a political solution to the Yemen conflict is that even though the conflict began as a localized affair, it has become part of a larger narrative of regional confrontation between Iran and its proxies on one side and the United States and Gulf monarchies on the other. According to one unnamed Saudi official, "The kingdom does not want to be dragged for much longer into war [in Yemen]…. But amid all the tension with Iran, Saudi Arabia does not want to look weak or show that it is hurting."66 Even if regional tensions cool, the Houthis and the Saudi-led coalition appear to 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 Houthis seem determined to outlast their opponents while consolidating their control over northern Yemen.

Although the international community, including the United States, continues to support Yemen's unity, the question of how best to share power between a central authority and Yemen's various regional power centers remains unresolved. Fundamentally, Yemenis disagree over whether or how to create an effective federal system and provide security in Yemen. Members of the international community also appear to disagree over questions of who may legally use armed force in Yemen. With so many de facto authorities across Yemen wielding military force of some type, the disarmament, demobilization, and reintegration of Yemen's various militias into a centrally led security force that international actors might partner with to counter terrorism seems an unlikely prospect for the near term.

Author Contact Information

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



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.


ACLED data suggests that civilians are less likely to be killed in political violence now than during previous points in the conflict and that Saudi coalition airstrikes–particularly during 2015–have been responsible for two-thirds of the civilian deaths attributable to direct targeting by conflict actors. For ACLED's monthly tally of total reported fatalities, see:


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 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.


See J.E. Peterson, Arabian Peninsula Background Notes APBN-006, "The al-Huthi Conflict in Yemen," published on, August 2008.


Refueling operations began on 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.


"Yemen Airstrike deaths top 100; Scores of Bodies have been recovered after a Saudi-led Attack on the Rebel-Run Prison," Los Angeles Times, September 3, 2019.


"Red Cross says more than 100 People killed in Airstrike on Yemen Prison," The Guardian (UK), September 1, 2019.


Report of the Group of Eminent International and Regional Experts as submitted to the United Nations High Commissioner for Human Rights - Situation of human rights in Yemen, including violations and abuses since September 2014 - A/HRC/42/17, September 3, 2019.


"Yemen's Houthi Group says will target UAE, Saudi Vital Military Facilities," Reuters, May 19, 2019.


In January 2018, the UN Panel of Experts on Yemen identified military unmanned aerial vehicles that are of Iranian origin (Ababil-T/Qasef-1) and were brought into Yemen after the imposition of the targeted 2015 arms embargo. See, 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 (S/2018/68) [EN/AR].


"Ansar Allah "Airport for Airport" Strategy underlines Potential for Re-Escalation of Yemen Conflict, Jane's Terrorism & Insurgency Monitor, June 21, 2019.


"Yemen rebel long-range arsenal grows lethal," Middle East Online, July 23, 2019.


"Yemeni Rebels unveil Cruise Missile, Long-Range UAVs," Jane's Defence Weekly, July 8, 2019.


"Saudi Oil Attack Photos Implicate Iran, U.S. Says; Trump Hints at Military Action," New York Times, September 15, 2019.


In 1839, the British Empire captured the southern Arabian Sea port of Aden, which it held, including some of its surrounding territories, until 1967.


For the translated text of 2011 GCC Initiative, see:


Charles Schmitz, "Yemen's National Dialogue," Middle East Institute, March 10, 2014.


"Yemen's Would-Be Model, Aden plagued by Bombs, Instability," Associated Press, December 24, 2016.


The United Arab Emirates has played a key role in countering AQAP throughout southern Yemen through both direct military intervention and the buildup of local proxies to hold territory liberated from AQAP. In April 2016, U.S. Special Operations Forces in Yemen reportedly worked with the UAE to defeat AQAP fighters at the port of Mukalla. UAE personnel have trained, equipped, and paid thousands of Yemenis to join various provincial militias in governorates across southern Yemen to combat AQAP. However, according to one Associated Press report, the UAE also has paid fighters from Ansar al Sharia (designated by the State Department in 2012 as an alias for AQAP) to join UAE-backed Yemeni groups. See, "Details of Deals between US-backed Coalition, Yemen al-Qaida," Associated Press, August 6, 2018. Another Associated Press report notes that "One Yemeni commander who was put on the U.S. terrorism list for al-Qaida ties last year continues to receive money from the UAE to run his militia, his own aide told the AP. Another commander, recently granted $12 million for his fighting force by Yemen's president, has a known al-Qaida figure as his closest aide." See "Investigation: Yemen war Binds US, Allies with al-Qaida," Associated Press, August 6, 2018.


"UAE runs Aden as Protectorate, while Hadi hides in the Shadows," Middle East Eye, November 27, 2017.


"Exclusive-UAE scales down Military Presence in Yemen as Gulf Tensions flare," Reuters, June 28, 2019.


"The UAE Revisits Its Foreign Policy Goals with New Tactics," Stratfor, August 13, 2019.


"AP Explains: How Emirates Troop drawdown impacts Yemen's war," Associated Press, July 25, 2019.


"After Aden: Navigating Yemen's New Political Landscape," International Crisis Group, Briefing 71, August 30, 2019.


Elana DeLozier, "Houthis Kill Top UAE-Backed Separatist Yemeni Commander," The Washington Institute, PolicyWatch 3158, August 1, 2019.


"UAE carries out Air Strikes against Yemen Government Forces to support Separatists," Reuters, August 29, 2019.


Alexandre Mello and Michael Knights, "Yemen's Fragile Military Balance," The Washington Institute, PolicyWatch 3173, September 3, 2019.


"Saudi Arabia defends Yemen Government against UAE-backed Separatists," Reuters, September 5, 2019.


For the full text of UNSCR 2216, see: [].


"Cracks in Saudi-UAE Coalition risk New War in Yemen," Associated Press, September 6, 2019.


According to the U.S. Energy Information Administration, "an estimated 4.8 million b/d of crude oil and refined petroleum products flowed through this waterway [Bab al Mandab] in 2016 toward Europe, the United States, and Asia, an increase from 3.3 million b/d in 2011. The Bab el-Mandeb Strait is 18 miles wide at its narrowest point, limiting tanker traffic to two 2-mile-wide channels for inbound and outbound shipments. Closure of the Bab el-Mandeb could keep tankers originating in the Persian Gulf from reaching the Suez Canal or the SUMED Pipeline." See EIA, "Three important oil trade chokepoints are located around the Arabian Peninsula," August 4, 2017.


The Ras Isa floating terminal refers to a floating oil tanker known as the Safer floating storage and offloading terminal owned by the state-run Yemen Oil and Gas Corporation. The 43-year-old tanker is moored several miles off-shore from Ras Isa and had been deteriorating for years. It holds an estimated 1 million barrels of crude oil. If it were to critically fail, it would not only cause serious environmental damage to the Red Sea, but would possibly put supplies of drinking water in danger due to its proximity to desalination plants. See, "Millions will go without Drinking Water if decaying Yemeni Oil Tanker Explodes," The Independent (UK), July 31, 2019.


Statement by the Chair of the Redeployment Coordination Committee, United Nations Mission to Support the Hudaydah Agreement (UNMHA), May 12, 2019. Also, see "Yemen President slams U.N. Envoy's handling of War in Letter to Secretary-General," Reuters, May 24, 2019.


"No Houthi military in three Key Yemen Ports for past Month: U.N.," Reuters, June 12, 2019.


United Nations, Briefing of the Special Envoy of The United Nations Secretary-General for Yemen to the Open Session of the Security Council, August 20, 2019.


United Nations, Redeployment Coordination Committee (RCC) Joint Press Statement - The Sixth Joint RCC Meeting, September 9, 2019.


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


"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.


International Crisis Group, Yemen Update #8, April 5, 2019.


"Saudi Arabia announces Capture of an ISIS leader in Yemen in U.S.-backed Raid," Washington Post, June 25, 2019.


The White House, Text of a Letter from the President to the Speaker of the House of Representatives and the President Pro Tempore of the Senate, June 11, 2019.


"Yemen's Anti-al Houthi Coalition is Collapsing, and America's Gulf Partners are Partially to Blame," American Enterprise Institute, August 13, 2019.


"Isis Blooper Video shows Terrorist repeatedly Interrupted by Squawking Bird," The Independent (UK), August 15, 2019.


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


"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.


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


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


"Iran's Khamenei meets Yemen Rebels after Blow for Saudi Coalition," Agence France Presse, August 14, 2019.


"Introduction to Just Security Series on UN Yemen Report," Just Security, September 12, 2019.


See CRS Report R45046, Congress and the War in Yemen: Oversight and Legislation 2015-2019, by Jeremy M. Sharp, Christopher M. Blanchard, and Sarah R. Collins.


Bruce Riedel, "Four Years on, Yemen War remains Saudi Arabia's Albatross," Al Monitor, March 21, 2019.


"Al Qaeda in the Arabian Peninsula (AQAP) in Yemen: A Continued Threat?" The Armed Conflict Location & Event Data Project (ACLED), September 8, 2018.


Department of State, Secretary Pompeo's Meeting With UN Special Envoy of the Secretary-General for Yemen Martin Griffiths, Office of the Spokesperson, May 18, 2018.


Department of State, Statement by Morgan Ortagus, Spokesperson, August 8, 2019.


"US official says Washington in Talks with Yemeni Rebels," Agence France Presse, September 5, 2019.


Op. cit., Text of a Letter from the President to the Speaker of the House of Representatives and the President Pro Tempore of the Senate.


"US Patriot deployment to Saudi Arabia confirmed," Jane's Defence Weekly, July 25, 2019.


Department of State, Press Statement: Houthi Attack on Abha Airport in Saudi Arabia, July 2, 2019.


For example, see CRS Report RL33533, Saudi Arabia: Background and U.S. Relations, by Christopher M. Blanchard.


Letter from Secretary of State Michael R. Pompeo to Senate Foreign Relations Committee Chairman James E. Risch, May 24, 2019.


Department of Defense, CENTCOM Yemen Strike Summary Jan. 1 – Apr. 1, 2019, Release No: 19-021 April 1, 2019.


"Push for Cease-Fire Stalls in Yemen --- Feud between Iran- allied Houthis and Saudi-led Forces Risks Stoking Regional Conflict," Wall Street Journal, August 7, 2019.