Editor’s Note: Fatima Abo Alasrar writes at The Ideology Machine, a publication on authoritarian information systems and Middle East policy, and is a Senior Analyst at the Washington Center for Yemeni Studies.

By: Middle East Program Team

In their most ambitious ground offensive in years, the Houthi militia has captured the port of Mocha and nearby islands to cement their control over Bab al-Mandab, the narrow corridor connecting the Red Sea to the Gulf of Aden. The move puts pressure on commerce through the Red Sea as the broader war with Iran has already choked traffic through the Strait of Hormuz.

This kind of escalation was not unexpected. But the U.S. decision to go to war with Iran in February was the catalyst, opening a Pandora’s box whose consequences are now playing out across the region. Before that, the Iran-backed Houthis had limited their attacks on Saudi Arabia under a Saudi-Iran agreement and had limited internal expansion under informal understandings after a  2022 UN-brokered truce collapsed. But all these agreements crumbled after the funeral of Ayatollah Ali Khamenei in June and the Saudi decision, with political support from the Trump administration, to target Sanaa airport to prevent the landing of an Iranian plane carrying the Houthi delegation that had attended the funeral. The Houthis responded by firing missiles at Saudi territory, and a week later, they began launching attacks on Saudi-linked tankers in the Red Sea.

The escalation follows the Trump administration’s decision to try to further constrict the Iranian economy through a naval blockade and new sanctions that Washington has dubbed Operation Economic Outcast. Iran had warned more than once that Washington would pay a price at Bab al-Mandab for refusing to acknowledge Iranian authority in Hormuz; the week before the offensive, Iran told the Houthis to step up their attacks on Saudi Arabia, promising more money, weapons, and personnel, according to Iranian sources cited by Reuters.

Senior commanders from the Islamic Revolutionary Guards Corps (IRGC) were already in Yemen, helping direct the push down the coast. Iran’s parliament speaker, Mohammad Bagher Ghalibaf, was quick to celebrate the September 10 fall of Mocha, writing the same day that the Yemeni people would “certainly prevail.” Tehran claims that the decision to take Mocha was solely the Houthis’ while acknowledging that the offensive served Iran by boosting oil prices and adding to the political costs of the war on both Washington and Riyadh.

Strategically, the timing made sense for the Houthis and Iran as four developments turned a long-held Houthi ambition into an opportunity.

The first is that the crisis at Hormuz had lost some of its edge. Traffic through the strait had collapsed to a trickle, but the market panic had subsided somewhat as the international community adapted and found alternate routes to circumvent the strait. Signals from the Trump administration about ending the war also affected the markets. In early August, talk of a deal to reopen the strait was enough to push Brent down to about $80 a barrel. When the U.S. then intensified sanctions, the leadership in Tehran realized that squeezing Hormuz was not enough to force an end to the war.

Second, the closure of Hormuz made the Red Sea Saudi Arabia’s principal alternative export route, increasing the appeal of the Bab al-Mandab to showcase Iranian leverage via the Houthis.

The week that Mocha fell was telling. In the space of three days, Washington destroyed five Iranian tankers, Iran claimed strikes on 10 vessels near Hormuz, and the Houthis took Mocha. Taken one at a time, these look like naval tit-for-tats. Taken together, they constitute a single response executed across two chokepoints. Of the two economic wars underway, Iran’s is arguably the better designed at least for now.

Third, Saudi Arabia’s consolidation of the anti-Houthi camp had given the internationally recognized Yemeni government new confidence. The South is now under a single Saudi-backed command structure, a shift I wrote about for Stimson earlier this year. But rather than waiting to see if this reorganization would translate into actual military strength, the Houthis preempted it. They pushed down the coast to shatter the government’s new defensive posture before it could alter the balance of power.

Finally, the Houthis had been preparing for this advance not just by holding back the firepower they used sparingly at the onset of the Iran-US war, but also through manpower as the movement has been running mobilization campaigns in every governorate it controls.  Frequent parades put uniformed fighters on display nationwide. Tareq Saleh’s National Resistance Forces, among the best-armed formations in the anti-Houthi camp, had held Mocha for nearly a decade, yet it changed hands within hours with barely a fight. (Saleh is the nephew of Ali Abdullah Saleh, a longtime former president who allied with the Houthis in 2015 but switched sides in 2017 and was subsequently killed by a Houthi sniper.)

That the defense of Mocha was that thin was not an accident.  Saudi Arabia and the United States each expected the other to stop the Houthis, and neither did. As the Houthis closed in on Mocha, reports emerged that Saudi Crown Prince Mohammed bin Salman called President Trump twice to press for a U.S. attack. However, American forces, Trump officials told the Saudis, would stay focused on Iran and Hormuz. By the time Saudi jets struck on their own, the city had already fallen.

Trump’s refusal was not for lack of warning. In April, Ali Akbar Velayati, an adviser to Iran’s supreme leader, publicly stated that Tehran views Bab al-Mandab the same way it does Hormuz. In July, when the Houthis announced their embargo on Saudi shipping, President Trump shrugged off the threat, stating, “If something like that happens, we take care of it.” He continued to threaten action against the Houthis after they hit two Saudi tankers, warning that the next attack would bring “major military punishment” on the Houthis and on Iran. The Houthis have since set Saudi oil installations ablaze and taken Mocha, and the punishment has not come.

This inconsistency in the U.S. position vis-à-vis Tehran’s proxies means that the Yemeni government and Saudi Arabia have had to handle the Houthis largely on their own, and this is a consequential test for both. For the internationally recognized Yemeni government, continued losses to the Houthis could irreparably damage credibility at home and in Riyadh, shaking Saudi faith that the anti-Houthi camp it just reorganized can hold together and perhaps pushing the Saudis toward a deal with the Houthis if that starts to look like the less painful option. The Houthis understand this, which is why they have already pushed on toward Dhubab and the Hanish Islands to take the rest of the coastline. Mocha is not going to be the end of the campaign.

Experience has demonstrated that conventional force alone cannot stop the Houthis, but sustained pressure can slow them down. Operation Rough Rider is a case in point, as once American strikes encroached on Houthi sites, the Houthis asked for a ceasefire within two months, a typical tactic when they feel military pressure.

Unfortunately for Yemen and the region, what lies ahead is likely another protracted conflict. Yemenis on the government side of the front lines will pay first, as shown in the loss of veteran commanders in Mocha. Saudi Arabia is absorbing Houthi attacks on its southern cities and oil facilities, which it does not want to sustain. And while the Houthis cannot defeat Saudi Arabia, they can play the same card they played with the Trump administration in 2025, making every response by their adversaries more expensive than the last, until restraint and a bad deal start to look cheaper than continued defense.

The lesson is clear. This is not an isolated problem or just a bilateral Saudi-Houthi or Saudi-Iranian conflict, and treating it as such gives Tehran the upper hand. This is an international problem, with a non-state actor seizing a port on the Red Sea to advance Iran’s — and its own — strategic goals. The same week Mocha fell, drones launched from Iraq knocked out Saudi Arabia’s East-West pipeline, the route that carries its crude to the Red Sea. It will take weeks to repair the damage.

This means that Washington cannot pretend that it is doing Riyadh a favor in facing proxies that have been instrumentalized to increase costs for the U.S. and the international community. Washington should start bearing some responsibility for the fallout that has continued to plague Yemeni waters after Operation Rough Rider. The Trump administration continues to impose strategic costs on Iran at Hormuz while ignoring Bab al-Mandab. The Islamic Republic has been eager to exploit the gap created by decoupling the Houthis from the war with Iran. Tehran understood long before Mocha fell that the two fronts cannot be separated, but Washington is running out of time to catch up.