In response to the attacks on ships and vessels in the Red Sea by the Iran-backed Houthi rebel group in Yemen, the US-led naval coalition Operation Prosperity Guardian, which includes Bahrain, Canada, France, Italy, the Netherlands, Norway, Spain, the Seychelles and the UK, bombed more than a dozen Houthi-controlled sites mainly in and near Yemen's capital, Sanaa, on Friday.

This marks a significant escalation after weekslong attacks by the Houthis, who are acting in support of the Palestinian cause and the militant Islamist Hamas group in Gaza.

The Houthis have said they will continue to attack every vessel on its way toward Israel until the Israeli Defense Forces lift the blockade on the Gaza Strip and allow the delivery of food and other essentials. 

Shortly after the US and UK-led strikes, the Houthis vowed retaliation.

"The battle will be bigger ... and beyond the imagination and expectation of the Americans and the British," The Associated Press news agency reported, quoting high-ranking Houthi official Ali al-Qahoum.

Yemen's long war

The Houthis derive from a tribal group out of northern Yemen, near the border with Saudi Arabia.

By religious sect, the Houthis are Shiite Muslims, but they belong to a specific branch called the Zaydi Shiites.

As such, they have beliefs that set them apart from mainstream Shiite Muslims. For instance, they do not believe in the return of a messiah-like figure, the 12th imam. The 12 imams are considered to be the descendants of the Prophet Muhammad, and the 12th imam is considered to have vanished but is expected to return one day.

Nonetheless, the fact that the Houthis are Shiite Muslims is important because this connects them with Iran, the country generally considered to represent Shiite interests in the region.

Zaydi Shiites make up about one-third of Yemen's population, and their political and military movement goes back to the 1990s. The contemporary movement was founded by Hussein al-Houthi, a former Yemeni politician who opposed the policies, and alleged corruption, of former Yemeni president Ali Abdullah Saleh, who was himself a Houthi. The group are named after Hussein al-Houthi.

After the Arab Spring protests of 2011 toppled Saleh's regime, the Houthis increasingly accused Yemen's new government — now headed by a Sunni Muslim — of marginalizing Zaydi Shiites. They also believed that the central government was too close to the US and thereby Israel, and that the current leader, Abed Rabbo Mansour Hadi, was also a Saudi stooge.

The Houthis rebelled against Hadi's unpopular government in 2014 and began to take over large parts of the country, including Sanaa. For the Saudis, who did indeed support Hadi, this was a major problem and they began to fight against the Houthis. The Saudis have been heading an international coalition fighting against the Houthis since 2015, but without great success.

In 2022, the opponents negotiated a six-month cease-fire. Even though this has since ended, the situation has remained comparatively calm in Yemen as all parties seemed to have come to the conclusion that they're at a stalemate.

The war in Yemen has been described as the world's worst humanitarian crisis by the United Nations.

What Houthis believe

The Houthis' ideology can be deduced from their motto: "God is great, death to the US, death to Israel, curse the Jews, and victory for Islam."

In their territory in northern Yemen, they have adopted a strict Islamist order with an anti-Western and anti-Israel bent.

Since the 1990s, successive Yemeni governments have supported calls for Palestinian statehood and an end to the Israeli occupation. This was in common with most nations in the Middle East. The Houthi group has further radicalized this position, and have found the support of many sympathetic locals. 

The Houthis are now considered close allies of the government in Iran. They see themselves as part of the so-called Axis of Resistance, an Iran-led regional alliance that also includes Hamas in Gaza, Lebanon's Hezbollah and various Iraqi paramilitary factions.

There are notable differences between the Houthis and those other groups, said Hamidreza Azizi, a researcher at the German Institute for International and Security Affairs. They are less dependent on Iran than groups like Hezbollah, he told DW.

It is impossible to know exactly how much support the Houthis get from Iran, or how much they respond to Tehran's orders. It's doubtful that Iran played a role in these latest attacks on ships in the Red Sea, Fabian Hinz, a research fellow for defense and military analysis at the International Institute for Strategic Studies, told DW.

Although shipping has been endangered, observers suggest the Houthi attacks don't pose much military danger to Israel itself. Any rockets fired in that country's direction have been repelled or shot down.

Rather, the attacks are a kind of political message for domestic audiences, according to Farea al-Muslimi, a research fellow with the British think tank Chatham House's Middle East and North Africa program.

"This war is a golden opportunity for the Houthi group to demonstrate its pro-Palestine, anti-Israel and anti-American position to its local population," said al-Muslimi. But their actions are unlikely to open any substantial new front for Israel to fight on, he added.

Global shipping in dire straits?

It's a different story for maritime traffic, though.

Connecting the Gulf of Aden with the Red Sea, the Bab el-Mandeb Strait is one of the most important in the world. It sees about 12% of world shipping traffic transiting here, on their way to the Suez Canal, the shortest shipping route between Europe and Asia.

To get there, vessels must pass off the coast of Yemen.

In response to the Houthi attacks, several major international freight companies have announced they won't be sending any more ships through the Bab el-Mandeb Strait and instead reroute them around the Cape of Good Hope. That adds about 3,500 nautical miles (6,482 kilometers) to a ship's journey to Europe from Singapore.

This article was originally written and published in German on December 20, 2023. It was updated on January 12, 2024 to reflect the latest developments.