Since mid-November, the Houthis, a Yemeni rebel group allied with Hamas and backed by Iran, have launched dozens of attacks on ships sailing through the Red Sea and the Suez Canal, a crucial shipping route through which 12 percent of world trade passes.

Early Friday morning, the United States and a handful of allies, including Britain, struck back, carrying out missile strikes on Houthi targets inside Yemen and thrusting the rebels and their long-running armed struggle further into the limelight.

The attack on Houthi bases came a day after the United Nations Security Council voted to condemn “in the strongest terms” at least two dozen attacks carried out by the Houthis on merchant and commercial vessels, which it said had impeded global commerce and undermining navigational freedom.

Here’s a primer on the Houthis, their relationship with Hamas and the attacks in the Red Sea.

Who are the Houthis?

The Houthis, led by Abdul-Malik al-Houthi, are an Iran-backed group of Shiite rebels who have been fighting Yemen’s government for about two decades and now control the country’s northwest and its capital, Sana.