After four years of relative calm, the war pitting Yemen’s Houthi militia against the country’s internationally recognized government and its backer Saudi Arabia is raging again.

In launching its full-scale military campaign against the Houthis in early October, the Saudi-led force said its goal was to “eliminate” the group. It’s an ambitious aim. Once dismissed as a ragtag band fighting in sandals from pickup trucks, the Houthis have demonstrated staying power and reach. Having taken over the capital Sanaa in 2014, the Houthis now control land containing most of Yemen’s population. They’ve previously withstood years of Saudi-backed military efforts to dislodge them as well as US, UK and Israeli bombing raids meant to punish the group’s attacks on commercial shipping in the Red Sea and on Israel itself.

While the Houthis have long received military assistance from Iran, they’ve found other ways to arm themselves. They have demonstrated growing military sophistication and, since the war restarted, have landed serious blows on Saudi cities as well as on oil giant Aramco’s headquarters.

Officially known as Ansar Allah, or Supporters of God, the Houthis are part of a clan that hails from Yemen’s northwestern Saada province. They’re followers of the Zaidi branch of Shiite Islam, which accounts for roughly a third of the country’s population.

The Houthis emerged in the 1990s after North Yemen and South Yemen were unified, waging a series of rebellions against the government. Their seizure of Sanaa in 2014 triggered a civil war that still divides the country.

They have imposed a repressive rule over Yemenis. They’ve recruited children as soldiers and have been accused by human rights groups of torturing opponents and persecuting religious minorities.

The Houthis are anti-West and anti-Israel, and are designated terrorists by the US and the European Union. They’re part of the so-called axis of resistance, which was established by Iran and includes Hezbollah in Lebanon and Hamas in Gaza, both of which are also classified as terrorist organizations by the US and others. These groups receive training, technical expertise and weapons from Iran.

The Houthis coordinate closely with Iran and largely share its strategic objectives, but they make their own decisions. Iran is an important source of weapons for the Houthis, but not the only one. They can draw upon tribal smuggling networks inside Yemen and are increasingly sourcing commercially available components and raw materials from further afield, including China. The group has expanded efforts to assemble and manufacture its own arms. By reducing their dependence on shipments of complete Iranian weapons, the Houthis have made it harder for adversaries to disrupt their operations.

By 2022, both sides in the Yemen war had reason to step back from the fighting. Saudi Arabia had intervened in the war in 2015 with the goal of restoring the internationally recognized government to power. But the Houthis remained entrenched and were striking back at Saudi Arabia using missiles and drones. For the Houthis, a break in the fighting offered the opportunity to secure concessions including more fuel imports and the right to operate limited commercial flights from Sanaa’s airport. A United Nations-brokered truce largely put a stop to cross-border attacks. Although it formally expired six months later, the uneasy calm held for almost four years.

Then, on July 13 of this year, Saudi jets struck Sanaa’s airport to stop an Iranian aircraft carrying a Houthi delegation from landing. The delegation was returning from the funeral of Iran’s late supreme leader, Ali Khamenei, who was killed at the beginning of the US and Israeli war on Iran. Saudi Arabia has long accused Iran of using commercial passenger planes as an air bridge to move weapons and military experts into Houthi areas of Yemen.

The Houthis responded by launching missiles and drones at Abha International Airport in southern Saudi Arabia. On July 20, they announced what they called a “naval blockade” of Saudi Arabia, warning shipping companies that their vessels risked being attacked if they used the kingdom’s ports. They then resumed an earlier practice of striking ships in the Red Sea, this time focusing on those they defined as Saudi-linked.

The militia followed up by attacking Saudi cities, military positions and oil infrastructure, provoking retaliatory Saudi airstrikes. Inside Yemen, the Houthis stepped up their campaign against the Saudi-backed government.

In September, in their biggest territorial advance in years, they pushed south, strengthening their control over Yemen’s Red Sea coast and the strategic Bab el-Mandeb strait, an important oil export corridor. Undoing those gains was high among the goals of the campaign launched in early October by the Saudi-backed Yemeni forces.

The campaign has included strikes on Houthi-controlled oil facilities in Sanaa, which the militia says provoked its attack on Aramco’s headquarters.

For Saudi Arabia, defeating the Houthis would eliminate a longstanding enemy of the kingdom. The militia’s attacks risk undermining the economic ambitions of the kingdom’s de facto ruler, Crown Prince Mohammed bin Salman. To diversify the Saudi economy away from oil, he wants to attract billions of dollars of foreign investment in projects ranging from data centers to electric vehicle manufacturing.

For other countries, the Houthis’ downfall would remove a threat to shipping that has disrupted traffic in the Red Sea for years. When the Houthis first began to attack vessels there in 2023, they said it was in retaliation for Israel’s military campaign in Gaza that followed the Oct. 7 Hamas attacks. The group originally said it was only focused on vessels with links to Israel. But ships without a direct connection were also hit. The Houthis had suspended their Red Sea attacks for nine months, after a Gaza ceasefire agreement was reached in October 2025.

The shipping route via the Suez Canal, Red Sea and Bab el-Mandeb is the most convenient passage for ships traveling between Europe and Asia. But to avoid the Red Sea altogether, many shipping firms now send their vessels around the southern tip of Africa instead — an expensive diversion that’s thousands of miles longer and can add two weeks to journeys.

The sheer size of Saudi Arabia makes the kingdom difficult to protect from aerial bombardment. The world’s 12th-largest country, it covers more than 2.1 million square kilometers (830,000 square miles) encompassing many strategic targets, including oil facilities, air bases and several large cities. The most recent Houthi strikes on the kingdom have tended to involve a mix of weapons — small drones; cheap, low-flying cruise missiles; and ballistic missiles — that further complicates defensive efforts.

Saudi Arabia’s spending on defense outstrips that of its neighbors, including Israel, Turkey and Iran, and even France and Italy, according to the Stockholm International Peace Research Institute. The kingdom operates Patriot missile batteries, flies F-15 fighter jets customized for its air force, and — alone among Gulf states — has mid-air refueling aircraft. However, the Saudi military is still in the process of modernizing. “Modernization is slow and confined to pockets of bright spots rather than upskilling across the force,” said Bloomberg Economics defense lead Becca Wasser.

The Houthis, meanwhile, are battle-hardened. They have survived years of airstrikes and widespread destruction in Yemen, giving them a far higher tolerance for the costs of war than Saudi Arabia. That asymmetry works in their favor.

In response to Houthi attacks on Red Sea shipping, the US in early 2025 launched more than 1,000 strikes on targets in Yemen over three months. But it’s difficult to hunt down the hidden, mobile launchers the Houthis use to fire missiles and to find and destroy arms production facilities they bury in the ground, especially in the rugged terrain in which the group operates. The US campaign ended with a ceasefire.

The Saudi government has sought help from friendly countries to counter the Houthis. The response has been tepid, suggesting a lack of enthusiasm to invest seriously in a fight against such a resilient foe.

Gulf states have issued statements supporting the kingdom but have stopped short of joining the war. Egyptian Foreign Minister Badr Abdelatty told Bloomberg Television that his country was ready to offer Saudi Arabia support, without providing specifics.

Turkey and Pakistan, both of which agreed to a defense pact with Saudi Arabia in August, have signaled they’re willing to send troops or weaponry to the kingdom but not in an offensive capacity.

The UK has provided an aircraft to help Saudi fighter jets refuel in mid-air and said it would deploy planes to shoot down Houthi missiles and drones. France said it would send troops and radar systems to defend Yanbu, the kingdom’s oil export hub on the Red Sea.

The US continues to give intelligence to the Saudis, but President Donald Trump has sought to avoid further military escalation in the Middle East ahead of his country’s Nov. 3 midterm elections.