For weeks, Houthi rebels in Yemen have launched drone and rocket attacks targeting ships in the Red Sea and the Bab al-Mandab Strait, a strategic passage that connects the Red Sea and the Arabian Sea. Below is a look at who the Houthis are, how they became such a formidable if unofficial military power, and why they are launching attacks on the vital trade route.

Who are the Houthi rebels and how many are there?

The Houthis are a Shiite Muslim sect with roots that date back centuries in Yemen. Members of the religion are a minority in Yemen, which is predominantly Sunni Muslim, but they are a significant one, numbering in the hundreds of thousands and making up as much as a third of the overall population.

Despite being minorities in the country, in 2012 Houthi rebels — numbering then in the low thousands — managed to capitalize on unrest in Yemen to build a loyal following in the north of the country. In 2014, they seized the capital Sanaa, sparking a civil war with the Western- and Saudi-backed government.

That war has continued since, despite limited cease-fires. A report in the Yemen Post from 2017 said the ranks of the rebel militia and administration, which refers to itself as Yemen's government, had swelled to roughly 100,000 people.

Do the Houthis control Yemen?

The Houthi administration now controls most of Yemen, including the capital Sanaa and the key Red Sea port of Hudaydah.

The Western-backed government has been dislocated to the southern port city of Aden, but it also controls the less-populated eastern portion of the country.

Are the Houthis a terrorist organization?

The Houthi movement has not been designated a terrorist organization by the U.S. government since 2021. The Biden administration has tried to walk a thin line between granting the group recognition as a legitimate political faction, in hopes of easing the war, while also backing the fight against it.

The veteran diplomatic envoy tasked by President Biden with finding a political solution to Yemen's bloody civil war said for the first time in 2021 that the U.S. recognized the Houthi rebels "as a legitimate actor," as Washington accepted that both sides in the conflict bore responsibility for the ongoing violence.

The remarks by Tim Lenderking were a clear overture toward the Houthi rebels.

"No one can wish them away or out of the conflict, so let's deal with realities that exist on the ground," Lenderking said, adding that in his experience, the Houthis had "spoken about a commitment toward peace in Yemen and I think there are certainly elements within the leadership that favor that."

The overture failed to bring peace to Yemen, however, and after Hamas' brutal Oct. 7 terror attack on Israel sparked the war in Gaza, the Palestinian group's traditional allies — including the Houthis and the Lebanon-based Hezbollah group, both of which are supported by Iran, like Hamas — have vowed to back up the Palestinian militants.

The Houthis, along with Hezbollah and Hamas, are part of a vaguely defined alliance that Iran refers to as "the axis of resistance" against Israel. All of the groups, like Iran, either dispute or reject Israel's right to exist as a nation and have regularly clashed with the close U.S. ally.

Why are the Houthis attacking ships in the Red Sea?

The Houthi movement said this week that its "naval operations" were being carried out "to support the Palestinian people in confronting the aggression and siege on Gaza." A spokesman added in a social media post that the rebel group did not intend the Red Sea attacks as "a show of force nor a challenge to anyone."

The Houthi rebels, who have a significant supply of ballistic missiles and Iranian-made attack drones, claim to be targeting ships belonging to Israel or the country's Western allies. U.S. warships in the region have shot down a growing number of attack drones launched from Yemen in recent days — including more than a dozen taken down on Dec. 16 alone.

Some vessels have been hit, but many of the rockets and drones launched from Yemen never reach their intended targets, and it's often not clear what those targets actually were before the weapons are destroyed.

The U.S. government estimates that almost 10% of the world's seaborne petroleum products passed through the Bab al-Mandab Strait in 2017, along with myriad other goods. The impact of the threat to shipping in the area has already been significant, disrupting the logistics of some of the world's biggest sea cargo lines and oil companies.

What is Operation Prosperity Guardian?

On Dec. 18, in Israel, U.S. Secretary of Defense Lloyd Austin announced a new joint military operation aimed at addressing "security challenges in the southern Red Sea and the Gulf of Aden, with the goal of ensuring freedom of navigation for all countries and bolstering regional security and prosperity."

Austin said the effort, dubbed Operation Prosperity Guardian, would see at least seven nations join the U.S., including the U.K., and several European Union allies, along with Bahrain and Canada. The operation's goal is to contribute militarily to policing the vital sea passages around Yemen's coastline and responding to attacks from Houthi-controlled Yemen.

"These attacks are reckless, dangerous, and they violate international law," Austin said during a trip to Israel. "This is not just a U.S. issue. This is an international problem, and it deserves an international response." 

The U.S. military is seeking greater international participation with the Guardian operation, but it's been created under the guises of the existing Combined Task Force 153, which was launched in 2022 with a virtually identical mission.

"Because this is a coalition of the willing, it's up to individual nations as to which parts of the combined maritime task force mission they will support," Pentagon press secretary Maj. Gen. Patrick Ryder told reporters last week. "We're working through that process right now, in terms of which countries will be participating in Task Force 153, and specifically what capabilities and types of support they will provide." 

CBS News' Kathryn Watson in Washington contributed to this report.

In:
• War
• Iran
• Red Sea
• Houthi Movement
• Hamas
• Israel
• Yemen
• Drone
• Missile Launch
• Middle East

Tucker Reals

Tucker Reals is cbsnews.com's foreign editor, based in the CBS News London bureau. He has worked for CBS News since 2006, prior to which he worked for The Associated Press in Washington D.C. and London.