Three years of civil war in Yemen have created the world's worst humanitarian crisis, with the United Nations estimating that 22 million people — three-quarters of the country's population — urgently need humanitarian aid.

But aid groups have seen their worst fears realized this week, as U.S.-backed forces organized by the United Arab Emirates launched an assault on the rebel-held port of Hodeidah — the entry point for 70 to 80 percent of the food, medicine, and aid supplies entering Yemen.

Oxfam has warned that a prolonged battle or siege would "massively escalate this humanitarian crisis while millions already are on the brink of famine," and the U.N. has said it would damage the prospects for long-term peace negotiations. Martin Griffiths, the U.N. peace envoy for Yemen, warned the U.N. Security Council that the assault "would, in a single stroke, take peace off the table."

The Intercept interviewed more than a dozen former White House and State Department officials, humanitarian leaders, and Yemen experts, many of whom characterized the offensive as a major failure by the U.S. to restrain its coalition partners, who are largely dependent on American weapons, intelligence, and logistical support. Those sources said the attack was a sign that the U.S. is allowing allies like Saudi Arabia and the UAE to drive American policy decisions in Yemen.