For the U.S., making sure maritime shipping lanes are kept safe and open is paramount. The Houthis now control territory on the coast of the Red Sea and the Bab el-Mandeb. The Bab el-Mandeb is a strait that at its narrowest point is just 18 miles across. It is impossible to traverse from the Mediterranean Sea into the Indian Ocean via the Suez Canal without going through the Bab el-Mandeb. Passage through the Suez Canal accounts for roughly 10 percent of all global shipping.
Yemen has become a haven both for al-Qaida and for offshoots of the Islamic State. The Iran-backed Houthis and the Saudi-backed government of Abed Rabbo Mansour Hadi are too busy fighting each other to deal with the situation, and Yemen is a lawless place awash in weapons of all kinds. To learn more about the various groups vying for territorial control in Yemen and how this intersects with the interests of regional powers, see our recent Reality Check.