Who are the Houthis and why did the US attack them?

The Houthi attacks on ships in the Red Sea following Hamas' Oct. 7 attack on Israel have riled commercial shipping and threatened to dangerously escalate heightened tensions in the Middle East.

On Thursday, the U.S. and the U.K. led a large-scale, retaliatory strike against the militants, hoping to degrade their ability to carry out attacks on vital waterways. But the group is already vowing to hit back.

Who are the Houthis, who are their allies, and what do they hope to achieve? Can the U.S. and allies contain the threat the militants pose to the region?

Officials and analysts break it down.

Rebels and de facto rulers in Yemen

The Houthis are a Shiite political and military organization that took form in Yemen during the 1990s as an opposition force to the Yemeni government.

Through the years, the group became increasingly inspired by anti-American and anti-Israeli sentiments coursing through the Middle East.

In 2011, the Houthis played a major role in sparking the Yemeni Revolution, which was born out of a wave of anti-government protests and uprisings known as the Arab Spring.

The revolution forced a transfer of power, but the Houthis were displeased with the newly installed leaders and in 2014 the group took control of Sanaa, the Yemeni capital, prompting an ongoing civil war that has ravaged the country.

A Saudi-led coalition intervened in the conflict with the stated goal of restoring the former rulers to power, but Yemen remains fractured. The Houthis retain control of Sanaa and large swaths of territory in western Yemen, but the group has failed to accomplish its aim of becoming the country's internationally recognized government.

The Yemeni civil war entered a cooling period in 2022, when the United Nations brokered a ceasefire between the warring parties. The conditions of the truce have largely held, but U.S. officials are concerned that reverberations from Israeli-Hamas war could lead to a rekindling of hostilities.

Iran's 'Axis of Resistance'

As the Houthis' control over Yemen has grown, so has the complexity and depth of their arsenal -- thanks to Iran, which has assembled an informal network of anti-American, anti-Israeli proxies dubbed "The Axis of Resistance."

Analysts say Iran capitalizes on groups like the Houthis, as well as designated terrorist groups Hamas and Hezbollah, to conduct indirect, irregular warfare against its enemies-- allowing Tehran to more effectively battle against better equipped adversaries like the U.S. and Saudi Arabia.

"The Iranians have been supporting the Houthis for more than a decade, probably at a pace of about $100 million per year," said Jon B. Alterman, a former State Department official and the director of the Middle East Program at the Center for International Strategic and International Studies.

"One of the Iranian government's innovations in recent years has been to support regional forces that they do not actually control. Their efforts are attributable but deniable, and the Iranians feel they enjoy benefits without paying the costs," he continued.

Trouble in the Red Sea

During the most intense years of Yemen's civil war, the Houthis stockpiled improved drone technology, advanced munitions, and anti-ship missiles provided by Iran--using the weapons to strike at their common enemy, Saudi Arabia, and its coalition.

Though they were still outgunned, the Houthis were able to launch effective strikes against Saudi Arabian oil tankers and disrupt the flow of oil and other resources to and from the immediate region.

In the aftermath of Hamas' attack on Israel, the Houthis have repurposed that strategy, launching attacks on more than two dozen ships transiting through commercial lanes in the Red Sea and the Gulf of Aden, according to U.S. Central Command.

The group also seized a Japanese vehicle carrier as well as its 25-person crew in November and is still holding the ship and the seafarers hostage.

The Houthis claim their aggression in the Red Sea is in support of the Palestinians, that militants are only targeting vessels with ties to Israel and say the attacks will only stop when the Israeli siege of Gaza ends.

However, according to the governments of U.S. and Israel as well as international registries that track commercial shipping movements, many of the vessels that have come under Houthi fire are not linked to Israel at all.

After carrying out strikes on sites used by the Houthis to launch maritime strikes, the Pentagon said there were "early indications are that the Houthis' ability to threaten merchant shipping has taken a blow."

But the Houthi's weapon systems are mobile and can be launched from small watercraft and trucks, so U.S. officials anticipate the group has retained ample firepower to follow through on its promise to retaliate for Thursday's bombardment and perhaps continue its assault on commercial waterways.

"Targeting weapons storage depots is how the administration is trying to handicap the Houthis. But it remains to be seen what missiles and drones the Houthis have in store," said Behnam Ben Taleblu, a senior fellow at the Foundation for Defense of Democracies.

"Wars of the Middle East these days are all about resolve, and the Houthis have the intention to carry out their campaign," he added.

Tehran may also be motivated to increase its support to the Houthis. A spokesperson for Iran's foreign ministry condemned the actions of the U.S. and U.K. militaries and warned that they would fuel "insecurity and instability" in the region, according to Iranian media reports.

Can the US do more?

The White House released a joint statement with allied powers on Thursday, promising the U.S. will not hesitate to strike again if the Houthis continue to wreak havoc in the Red Sea

"Let our message be clear: we will not hesitate to defend lives and protect the free flow of commerce in one of the world's most critical waterways in the face of continued threats," the statement reads.

But some U.S. officials are worried that continuing to exchange volleys with the Houthis will restart the simmering conflict in Yemen or inspire other belligerents—like Hezbollah—to ramp up its war against Israel, potentially prompting a regional war.

On Friday, the Biden administration announced a new wave of sanctions aimed at disrupting the flow of supplies and finances from Iran to the Houthis.

Administration officials also say there has been some deliberation over whether the Houthis should be officially labeled as a terrorist group, but there is concern that the legal limitations that accompany the designation would inhibit the peace process aimed at resolving the Yemeni civil war.