Yemen’s Houthis and the expansion of Iran’s Axis of Resistance

Key Points

• Iranian-sourced nonnuclear proliferation in Yemen — ballistic missiles and unmanned aerial vehicles (UAVs) — is part of a larger pattern in the Middle East that tests the current regional security architecture. The Yemen conflict has provided Iran with a live-fire testing ground for longer-range capabilities. Houthi-fired Iranian-sourced ballistic missiles and UAVs provide data to feed back into Iranian weapons development cycles. Additionally, the Houthis have innovated new tactics with Iranian-sourced UAVs, tactics since adopted by Iranian-backed Iraqi militias, showing the transfer of knowledge between theaters.
• The Houthis’ expansion of the scope of Yemen’s conflict has created a growing requirement to defend US personnel based in the region and support Gulf partners against ballistic-missile and UAV attacks. The missile defense systems in place to counter the Iranian-sourced Houthi threat are expensive, especially compared to the relatively low-cost weapons the Houthis use. Counter-smuggling operations have had a limited impact. Targeting Iranian-sourced components to render them ineffective before they are transferred might produce more asymmetrical results.
• The United States must develop a comprehensive approach to Yemen and the region that reflects the new reality of the Houthis as part of Iran’s Axis of Resistance. The Houthis’ incorporation into the Axis broadens the means of action at Iran’s disposal to advance its regional interests, especially as Iran seeks to contest deepening Israeli-Emirati ties.

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Executive summary

Yemen’s Houthis are part of the Iranian-led informal alliance known as the Axis of Resistance and increasingly threaten regional security in the Middle East. US policy has framed the Houthis as an artifact of Yemen’s war—a local Yemeni movement with local aims or, alternatively, a Yemeni proxy under Iran’s full command. Instead, the Houthis have preserved their autonomy while integrating into Iran’s network of state and nonstate actors opposed to Western influence in the Middle East. Houthi ties with Iran and other Axis members have strengthened significantly during the past eight years of Yemen’s war, and Iranian-sourced capabilities transferred to the Houthis have expanded the conflict beyond Yemen’s borders. US policy has lagged behind these developments and does not reflect an understanding of Houthi or Iranian aspirations beyond Yemen’s civil war.

Shared interests underpin the relationship between the Houthis and Iran and the Axis of Resistance. Houthi leaders uphold Iran’s Islamic Revolution as a model to follow, and Iran’s revisionist ideas and efforts to reshape the regional order resonate with them. They thus have found common ground with other Axis members seeking to change the status quo through force, including Hezbollah and Iraqi Shi’a militias, among others. For Iran, the Houthis initially presented an opportunity to threaten Saudi Arabia’s southern border, and Iran has led an effort to cultivate the Houthis as part of its network. The Houthis now rely on Iran and the Axis to retain certain capabilities necessary for their ongoing projection of power from Yemen and have begun to support Axis initiatives from which they do not necessarily benefit.

Senior IRGC Quds Force and Hezbollah officials coordinate support to the Houthis. The effort to develop the Houthis’ military capabilities has transformed the Houthis’ threat. Previously, the Houthis could only defend their own territory. Now, they can project force far beyond Yemen’s borders. Iranian-sourced weapons include antiaircraft systems, ballistic missiles, short- and long-range UAVs, land-based IEDs, and WBIEDs. Many of these weapons were not present in Yemen before the war. A cadre of Quds Force and Hezbollah operatives are also on the ground in Yemen, training and advising the Houthis. Iran has formal diplomatic relations with the Houthi government, and Iranian diplomats have advanced Houthi interests on the international stage. Other Axis of Resistance members have developed relationships with the Houthis, hosting their representatives and promoting Houthi narratives. Additionally, IRGC- and Hezbollah-linked networks have provided the Houthis with financial support and fuel transfers. This report’s appendixes document the types of support by actor in detail.

Key takeaways

The Yemen conflict has provided Iran with a live-fire testing ground for longer-range capabilities. Iran has provided military assistance to its Iraqi proxies for longer but has transferred more-advanced weaponry to the Houthis. The threshold in Jerusalem, Washington, and elsewhere to tolerate the presence of sophisticated weapons may be higher for Yemen due to its location and the cover of the civil war. Houthi-fired Iranian-sourced ballistic missiles and UAVs feed data back into Iranian weapons development cycles. Additionally, the Houthis have innovated new tactics with Iranian-sourced UAVs—tactics since adopted by Iranian-backed Iraqi militias showing the transfer of knowledge between theaters.

The Houthis now threaten the security of Saudi Arabia and the UAE. Houthi attacks against Saudi Arabia increased notably in 2021, using ballistic missiles and UAVs to target primarily Saudi oil infrastructure, civilian airports, and military installations. Their ability to sustain such a campaign reveals a steady supply of weapons. Beginning in January 2022, the Houthis launched a campaign of strikes targeting sites in Abu Dhabi, UAE, which killed three civilians and threatened US service members based in Al Dhafra military base. Saudi Arabia and the UAE have used Patriot missile defense systems to defend against Houthi strikes, and the Emirati military has since fired its THAAD missile defense system two times. Both systems are expensive compared to the relatively low cost of the Houthis’ ballistic missiles and UAVs, creating a clear asymmetry advantageous to the Houthis.

Iran has incorporated the Houthis’ longer-range capabilities into its regional approach and may seek to stage attacks against targets farther afield, such as Israel. The absence of any real response to the September 2019 attack in Abqaiq, Saudi Arabia, that temporarily halved Saudi oil production shows how Iran has established an effective deterrence mechanism using plausible deniability and escalation risks. The Houthis publicly claimed credit for the attack, placing it within an escalation of the Yemeni war, yet subsequent US assessments showed the attack originated from the north, not the south. The proliferation of similar capabilities across the Axis has reduced the ability to ascertain rapidly and with confidence who perpetrated an attack. Iranian-sourced weapons within the Houthi arsenal can reach Israel, and the risk of an IRGC-coordinated multi-actor attack on Israel is rising as Iran seeks to contest the strengthening of ties among Sunni Arab states and Israel in a post–Abraham Accords environment.

US policy implications

The Houthis’ incorporation into the Iranian-led Axis of Resistance and their Iranian-sourced long-range capabilities present new challenges to American interests in the Middle East. Any successful approach to addressing these challenges must be part of a more comprehensive strategy for Yemen and the region. A strategy for Yemen must not only address the Houthi threat but also sustain pressure on al Qaeda and stabilize the country to prevent the further deterioration of humanitarian conditions. The United States must also help defend its regional partners, Saudi Arabia and the UAE, from further Houthi attacks. Regionally, the United States must account for how the Houthis could benefit downstream from the lifting or nonenforcement of sanctions on Iranian entities and for the possibility of coordination or cooperation among Axis members.

Successive US administrations have failed to stem the flow of Iranian support to the Houthis and the growing Iranian influence over them. The IRGC Quds Force transferred increasingly sophisticated weapons and capabilities to the Houthis during the Trump administration’s “maximum pressure” campaign against Iran. The threat of US sanctions was insufficient to deter the deepening of Houthi ties to the Iranian network. The emphasis on US diplomacy that has occurred under the first year of the Biden administration, coupled with a shift in the US approach to the Middle East, likewise has been problematic. US and UN officials have since sought Iranian assistance with the Houthis to negotiate an end to the war, even though Iran is not a belligerent. Today, Houthi interests are closely intertwined with those of the Axis of Resistance, and the Houthis depend on Iranian-sourced weapons to project power, making a policy of splitting them from Iran unlikely to succeed.

The growing Houthi threat has driven requirements for the defense of US personnel based in the region and defense support to Gulf partners. It is part of a larger pattern of Iranian-sourced nonnuclear proliferation that tests the current regional security architecture. Relatively low-cost UAVs serve as effective precision munitions at increasing ranges. Similarly, Houthi-fired ballistic missiles impose significant defense costs on regional partners. Defending against both will prove to be an expensive endeavor. Preventing the flow of weapons and materials to the Houthis will reduce the Houthi threat, but counter-smuggling operations have had limited impact. Iran almost certainly provides essential components for certain weapons. Rendering these components ineffective or less reliable directly may achieve more asymmetrical results on Houthi capabilities.

Yemen is now a single theater in a larger, regional war. The Houthis have developed extensive ties across the Axis of Resistance and have integrated Axis narratives into their own. Iran is waging proxy warfare through the Houthis, and Iran’s limited investment in them has expanded the scope of the conflict beyond Yemen’s borders. Weapons in the Houthis’ arsenal threaten Gulf states and Israel, as well as maritime traffic in the Red Sea and Gulf of Aden. Iran and its Axis of Resistance oppose the deepening of relations between Israel and Arab states, particularly the UAE, and have signaled they will contest these developments. Understanding the Houthis only within the context of Yemen misses this shift in regional security dynamics. The United States must change its approach to securing its interests in the Middle East given the new reality of the Houthis as part of the Axis of Resistance.

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