Yemen: Civil War and Regional Intervention

December 18, 2015 (R43960)
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This report provides material on the latest crisis in Yemen and the U.S. policy response. For further background and analysis on Yemen, see CRS Report RL34170, Yemen: Background and U.S. Relations, by [author name scrubbed].

In March 2015, Saudi Arabia and members of a coalition launched a military operation aimed at restoring the rule of Yemeni President Abdu Rabbo Mansour Hadi, who fled Yemen on March 25, 2015, after over a year in which his government and tribal allies have gradually been supplanted by an alliance comprised of the Houthi movement and loyalists of former President Ali Abdullah Saleh.

The White House issued a statement on March 25 blaming the Houthis for causing the crisis in Yemen. The United States recognizes President Hadi as the legitimate leader of Yemen, and President Obama authorized "the provision of logistical and intelligence support to GCC-led military operations." The Administration claimed that while U.S. forces are "not taking direct military action in Yemen in support of this effort, we are establishing a Joint Planning Cell with Saudi Arabia to coordinate U.S. military and intelligence support."

Although the Houthi-Saleh alliance had been gradually seizing control of Yemeni provinces and government/military installations for more than a year, in the winter 2015, they had rapidly outmaneuvered President Hadi, who had been under house arrest since January. Hadi eventually escaped from his Houthi captors and fled to Aden, where he denounced the coup against him and began to marshal the remains of the national military as well as loyal tribal militias to counter Houthi-Saleh advances.

As of December 2015, the United Nations estimates that the war has killed at least 5,878 people. The United Nations, represented by U.N. Special Envoy for Yemen Ismail Ould Cheikh Ahmed, has secured a commitment from all combatants to negotiate a peace deal. Formal talks began on December 15 in Switzerland; a cease-fire went into effect the same day. However, since the conflict began, previous agreed-upon cease-fires have been violated by all sides, with combatants continuing to fight for maximum territorial gains. As of December 18, reports indicate that fighting continues throughout Yemen, and peace talks in Switzerland have stalled.

There is a significant terrorist presence in Yemen, and U.S. policymakers are concerned that without a willing counterterrorism partner such as President Hadi, the United States may lack necessary intelligence cooperation on the ground to counter groups such as Al Qaeda in the Arabian Peninsula (AQAP) or the Islamic State.

Yemen: Civil War and Regional Intervention


In March 2015, Saudi Arabia and members of a coalition they established launched a military operation (referred to by the Saudis as Operation Storm of Determination or Decisive Storm) aimed at restoring the rule of Yemeni President Abdu Rabbo Mansour Hadi, who fled Yemen on March 25, 2015. Hadi's departure followed over a year in which his government and tribal allies were gradually supplanted by an alliance comprised of the Iran-supported Houthi movement1 and loyalists of the previous President, Ali Abdullah Saleh.

As of December 2015, the United Nations estimates that the war has killed at least 5,878 people. The United Nations, represented by U.N. Special Envoy for Yemen Ismail Ould Cheikh Ahmed, has secured a commitment from all combatants to negotiate a peace deal. Formal talks began on December 15 in Switzerland; a cease-fire went into effect the same day. However, since the conflict began, previous agreed-upon cease-fires have been violated by all sides, with combatants continuing to fight for maximum territorial gains. As of December 18, reports indicate that fighting continues throughout Yemen, and peace talks in Switzerland have stalled.

A Prelude to War

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 between 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 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 Abed Rabbo Mansour al 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, a National Dialogue Conference was convened to reach broad national consensus on a new political order. However, in January 2014 it ended without agreement.

One anti-government 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's conclusion, 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.

In 2014, Houthi militants took over the capital and violated several power-sharing arrangements. In 2015, Houthi militants placed President Hadi under house arrest. Although he was able to escape to Aden in southern Yemen, his position became untenable, as Houthi forces advanced from the capital all the way to Aden. 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.

Conflict Update

The current battle lines in Yemen have hardened, with the Saudi-led coalition and remnants of President Hadi's government controlling most of southwestern Yemen, including the port city of Aden. Yemen's third largest city, Taiz, has been the scene of fierce fighting in recent months. In November, the coalition launched a major offensive to retake the city and the areas surrounding it. The coalition has used air power and ground forces while the Houthis have blockaded the roads leading to Taiz, exacerbating an already bleak humanitarian situation for city residents. Moreover, many of the pro-government ground soldiers being used by the coalition to uproot the Houthis from Taiz are either tribal fighters or part of Salafist Sunni militias that are bent on waging a sectarian war against the Zaydi Shiite Houthis.2 Other reports indicate that the United Arab Emirates (UAE), a key coalition partner, is employing foreign mercenaries primarily from South America to serve as ground troops.3

The war also continues in other areas of Yemen. In the far north along the Yemeni-Saudi border, the Houthis continue to try and infiltrate the kingdom. In the Saudi provinces of Najran and Jizan, hundreds of Houthi fighters launched an offensive into Saudi territory and briefly captured Saudi border posts before being repelled by coalition forces. The Houthis have launched Scud and other ballistic missiles into Saudi territory and at coalition forces inside Yemen. Saudi Arabia and the United Arab Emirates each have multiple U.S.-supplied Patriot missile batteries protecting their respective forces. On December 14, just one day before peace talks began in Switzerland, Saleh-aligned forces launched an OTR-21 Tochka rocket at a Saudi-led coalition base, killing an estimated 154 coalition troops including a high ranking commander of the Saudi Special Forces in Yemen.

Figure 1. Lines of Control in Yemen: December 2015


The military conflict has reached a critical phase. Geographically, the Saudi-led coalition has retaken some of the lowland areas of southern Yemen (traditionally Sunni), while their tribal partners and Al Qaeda forces control the rest. The Houthis and pro-Saleh forces remain ensconced in the capital and the mountainous highlands of northern Yemen (traditionally Zaydi4). In fact, the lines of control now somewhat resemble the previous division of Yemen into two separate countries, a political situation that lasted from 1918 to 1990. The Saudi-led coalition now faces the difficult choice of pressing forward into more hostile terrain and, according to one analysis, "Further military movements, such as the push toward Sanaa, will likely impose an extreme cost — in casualties and materiel — on the attackers."5 The prospect of increased casualties on both sides could be a major factor in bringing the warring parties to the negotiating table.

Another factor creating battlefield stasis is the lack of cohesiveness of the Saudi-led coalition and its dependence on foreign ground forces and local Yemeni tribes and Islamists to secure liberated areas. In Aden, it is unclear whether the coalition has fully secured the city, as indicated by the recent assassination of the provincial governor there (see below). Another report suggests that Saudi Arabia and the UAE are in disagreement over Saudi's reliance on the Islah party, the Yemeni version of the Muslim Brotherhood.6

Iran's Role

Iran reportedly continues to support Houthi militias with weapons shipments. In late September, coalition naval forces, which have blockaded Yemen's ports, seized an Iranian fishing boat carrying, according to a coalition spokesperson, "18 anti-armored concourse shells, 54 anti-tank shells, shell-battery kits, firing guidance systems, launchers and binoculars' batteries."7 However, while the coalition's naval blockade has periodically intercepted or deterred Iranian arms shipments, it also has slowed the delivery of humanitarian aid. UNSCR 2216 authorized member states to prevent the transfer or sale of arms to the Houthis or to former President Saleh and also allows Yemen's neighbors to inspect cargo suspected of carrying arms to Houthi fighters. However, port cities still controlled by the Houthis, such as Hodeida on the Red Sea coast, have witnessed ships filled with food and fuel sitting off-shore, as Arab coalition vessels search them for illicit arms.8

Prospect for Peace?

As peace talks convene in Switzerland, perhaps the biggest obstacle to overcome is how to form a lasting national unity government that is acceptable to the major Yemeni and non-Yemeni players on the ground: the Houthis, the Saudis, the forces aligned with ex-President Saleh, and the current government. President Hadi, his Saudi backers, and the international community have insisted that all sides abide by the terms of United Nations Security Council Resolution (UNSCR) 2216 (April 2015), which, among other things, demands that the Houthis withdraw from areas they have occupied. UNSCR 2216 also stressed the necessity of resuming "Yemen's political transition process with the participation of all Yemeni parties in accordance with the Gulf Cooperation Council Initiative and its Implementation Mechanism and the outcomes of the comprehensive National Dialogue conference." However, according to analyst Bruce Riedel, "The current peace effort is based on a formula decided hastily by the Security Council to satisfy Riyadh."9 Since the Houthis believed that these previous processes did not take into account their demands for greater power, it is possible that negotiators in Switzerland may have to construct a new power sharing formula. If so, it may mean that the status of key Yemeni officials, such as current President Hadi and former President Saleh, may be in flux.

Humanitarian Situation

Yemen, which under normal circumstances is the least-developed country in the Arab world, is facing an unprecedented humanitarian crisis. According to the United Nations, more than half of Yemen's 25 million people are designated as "food insecure" and depend on food assistance for their survival. Six million Yemenis require immediate food assistance, and the United Nations warned that unless food assistance reaches Yemen in large quantities, Yemen may be on the brink of famine. To date, 2.3 million Yemenis are internally displaced persons (IDPs). Moreover, shortages of fuel used to pump water have led to a significant deterioration in public health, as dengue fever has broken out in Yemen's third-largest city of Taiz. On November 23, the United Nations Office for the Coordination of Humanitarian Affairs (OCHA) estimated that in 2016, approximately 82% of the population will require humanitarian assistance to meet their basic needs. In FY2015, the United States contributed $178.8 million in humanitarian aid related to the Yemen crisis.10


When Yemen is in the throes of domestic conflict and its military occupied, terrorist groups such as Al Qaeda in the Arabian Peninsula (AQAP) and the Islamic State (IS/ISIS/ISIL) have been able to seize territory in outlying provinces. This has been the case during the current war. In the early days of the conflict, AQAP militiamen, who already had been active in the eastern province of Hadramawt, attacked government installations, air and sea ports, and hydrocarbon facilities. AQAP seized the city of Al Mukalla in April. In December 2015, AQAP militiamen (known as Ansar al Sharia) took over two urban towns (Jaar and Zinjibar) in the province of Abyan, an area it had occupied in 2011. AQAP also is active in the coalition-occupied city of Aden, where the chaos that has engulfed the war-torn city has enabled Ansar al Sharia fighters to recruit openly.

Reports also suggest that groups nominally affiliated with the Islamic State are developing deeper networks inside Yemen. At least three IS-related groups have emerged in Yemen (Wilayat Sana'a, Wilayat Lahij, and Wilayat Aden-Abyan), although it remains unclear how much they coordinate with each other or with IS leaders based in Iraq and Syria. In December 2015, one IS group detonated a car bomb that killed the provincial governor of Aden. IS suicide bombers have repeatedly targeted mosques frequented by Zaydi worshippers and have cast themselves as defenders of Yemen's Sunni population. Some officials are concerned that as the Islamic State expands its reach in Yemen, it will become more of an external threat. According to Matthew G. Olsen, former director of the National Counterterrorism Center, "There's real concern that some of the most capable operational terrorists, who are now with AQAP, could join forces with ISIS and pose a heightened threat to carry out external attacks."11

U.S. Policy

The Saudi-led coalition's war in Yemen presents the Administration with a number of challenges. On the one hand, the Administration is supportive of the overall Saudi goal of restoring President Hadi's government to power. The Administration, like Saudi Arabia, does not want to see Houthi fighters who receive nominal Iranian aid rule large swaths of Yemen.12 Moreover, the Administration's position is that President Hadi is the legitimate internationally recognized President of Yemen, and U.S. diplomacy between 2011 and 2012 was critical in transitioning Yemen from Saleh's rule to Hadi's presidency. Hadi's government was considerably more reliable than Saleh's in countering terrorism, as President Hadi permitted the United States to conduct counterterrorism operations on Yemeni soil.

On the other hand, the Administration may question the Saudi-led coalition's methods for achieving the restoration of Hadi's rule, particularly as the civilian death toll continues to climb and the humanitarian situation devolves. Although the United States may be providing the Saudis and other coalition partners with key logistical aid and rearmaments, it is unclear how much leverage such support provides policymakers, particularly in the wake of the recently concluded Iran nuclear deal, which Saudi Arabia has tepidly approved.13 Furthermore, U.S. counterterrorism efforts in Yemen still rely on Saudi cooperation, leaving U.S. officials who wish to see a political settlement in Yemen little room to maneuver if Saudi Arabia continues to press forward with military operations.

For now, the Obama Administration continues to provide logistical assistance to the coalition,14 though the United States has pressed Gulf countries to assist in ameliorating Yemen's humanitarian crisis and called on all parties to move toward a political solution to the conflict. The United States and Saudi Arabia continue to cooperate in countering terrorism in Yemen, as the leader of Al Qaeda in the Arabian Peninsula (AQAP) was reportedly killed in a missile strike in June 2015.

The Use of U.S.-supplied Weaponry in Yemen

Several U.S. and international human rights organizations have reported that repeated Saudi Arabian air strikes have indiscriminately killed hundreds of Yemeni civilians and that Congress should cease approving related U.S. arms sales to the kingdom.15 In December, a Saudi airstrike struck a Doctors Without Borders medical clinic despite claims by the organization that it had recently provided Saudi officials with the coordinates of the clinic. According to Joe Stork, deputy director of Human Rights Watch's Middle East and North Africa division, "Until Saudi Arabia investigates apparently unlawful strikes by coalition warplanes and takes appropriate action, the US should not be supplying them more bombs.... Saudi disregard for the requirements of the laws of war makes enablers of those countries providing the weapons."16

The Obama Administration has acknowledged that civilian casualties from coalition air strikes are mounting, though U.S. officials are careful to point out that the Houthi movement bears responsibility for starting the war. According to State Department Deputy Spokesperson Marc Toner, "the Saudis are there conducting these airstrikes because of the ongoing violence stoked by Houthi rebels, but that said, there have been incidents where we've seen civilian casualties as a result of these airstrikes. Just like we do in conflicts around the world, we always call for restraint in conducting these kinds of airstrikes and express our concern when there are civilian casualties."17

Some lawmakers may be concerned about the deteriorating humanitarian situation in Yemen. In late September, Representative Ted W. Lieu wrote a letter to the new chairman of the Joint Chiefs of Staff advocating for a halt to U.S. support for the Saudi-led coalition until it institutes safeguards to prevent civilian casualties.18 In October 2015, 10 Members of Congress wrote a letter to President Obama urging him to "work with our Saudi partners to limit civilian casualties to the fullest extent possible."19 In October 2015, Senator Markey stated that "I fear that our failure to strongly advocate diplomacy in Yemen over the past two years, coupled with our failure to urge restraint in the face of the crisis last spring, may put the viability of this critical [US-Saudi] partnership at risk."20

In investigating the use of U.S.-supplied weaponry by coalition forces in Yemen, Congress may review the applicability of several authorities. Among others, Section 4 of the Arms Export Control Act (P.L. 94-329) (22 U.S.C. 2751 et. seq.), referred to as the AECA, defines the purposes for which military sales by the United States are authorized. It states that, among other things, defense articles and defense services shall be sold to friendly countries "solely for "internal security" and "legitimate self-defense." It should be stressed that the Arms Export Control Act as amended, the Foreign Assistance Act of 1961 as amended, and predecessor acts do not define such critical terms as "internal security" and "legitimate self-defense." It remains for the President or Congress to define the meaning of such terms as they may apply to the question of a possible violation by a foreign country of an applicable agreement governing the sale of U.S. defense articles or defense services.

Author Contact Information

[author name scrubbed], Specialist in Middle Eastern Affairs ([email address scrubbed], [phone number scrubbed])



The Houthi movement (also known as Ansar Allah or Partisans of God) is a predominantly Zaydi Shiite revivalist political and insurgent movement that formed in the northern province of Sa'da in 2004 under the leadership of members of the Houthi family. It originally sought an end to what it viewed as efforts to marginalize Zaydi communities and beliefs, but 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. Skeptics highlight the movement's ideological roots, its alleged cooperation with Iran, and the slogans prominently displayed on its banners: "God is great! Death to America! Death to Israel! Curse the Jews! Victory to Islam!"


"Yemen's Taiz Sinks into the Abyss as Salafis fight War of Revenge," Middle East Eye, December 2, 2015.


"Emirates Secretly Sends Colombian Mercenaries to Yemen Fight," New York Times, November 25, 2015.


Yemen's Zaydis take their name from their fifth Imam, Zayd ibn Ali, grandson of Husayn. Zayd revolted against the Ummayad 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. Moreover, it is doctrinally distinct from "Twelver Shiism," the dominant branch of Shi'a Islam in Iran and Lebanon.


"In Yemen, Talks Begin When Fighting Stalls,", December 9, 2015.


"Saudi Arabia's Yemeni Quagmire," Wilson Center, December 15, 2015.


"Weapons Bound for Yemen Seized on Iran Boat: Coalition," Reuters, September 30, 2015.


"Arab Coalition Navy Inspections Paralyze Yemen Food Shipments," Reuters, September 10, 2015. Reportedly, the United States has said that commercial vessels off the coast of Yemen should only be inspected when there are "reasonable grounds" to suspect illicit arms shipments. See, "U.S. tells U.N. it Wants to See Boost in Shipping into War-Torn Yemen," Reuters, September 30, 2015.


"How to end the war in Yemen," Al Monitor, October 27, 2015.


USAID, Yemen - Complex Emergency Fact Sheet #2, Fiscal Year (FY) 2016.


"Islamic State Gains Strength in Yemen, Challenging Al Qaeda," New York Times, December 14, 2015.


In late September 2015, two Americans held captive by Houthi fighters were released. The government of Oman reportedly served as an intermediary and helped secure their release.


"Saudi Arabia Satisfied with Obama's Assurances on Iran Deal," Reuters, September 4, 2015.


"Saudi-led Yemen Air War's High Civilian Toll Unsettles U.S. Officials," Los Angeles Times, April 16, 2015.


Some groups also have called on other foreign governments to suspend arms shipments to Saudi Arabia after alleging that coalition air strikes have struck civilian targets. Amnesty International has called on the British government to investigate the use of British-supplied aerial weaponry supplied to Saudi Arabia. See:


"US: Reject Bomb Sales to Saudi Arabia," Human Rights Watch, November 18, 2015.


U.S. State Department, Daily Press Briefing, November 10, 2015.


"Saudis Face Mounting Pressure Over Civilian Deaths in Yemen Conflict," New York Times, September 29, 2015.



"Senate Democrats hold up Arms Sales for Saudi war in Yemen," Al Monitor, October 7, 2015.