The level of intra-Muslim fighting in Yemen has advanced so far that the United States was forced Sunday to withdraw its presence from the country altogether.

The embassy in Sana’a, the capital, was closed in February. Now the Special Operations forces from a drone base, Al Anad, which the United States has been operating for years, have been withdrawn as well.

It is a general rule in judging the conduct of U.S. relations that, if America has important interests in a given country, those relations can survive a major change of government. But the answer in strategically located Yemen was clearly negative and a reflection of the degree and nature of U.S. involvement in Yemen’s internal affairs. In this case, the United States has been very involved, for years, and an important part of that role has been military- and intelligence-related.

Yemen had been ruled for 22 years by a dictator, Ali Abdullah Saleh. The United States was involved in forcing him out in 2012, to be replaced by Vice President Abdu Rabbu Mansour Hadi, whom Washington supported. Both leaders were Sunni Muslims, who make up two-thirds of Yemen’s population of 25 million. The Shiite Houthis have been in rebellion against the Sunnis for years and they finally succeeded in taking control of Sana’a in September.

Heavier fighting between Sunnis and Shiites made Sana’a and the drone base unsustainable for the United States and resulted in the Americans’ departure. It isn’t clear what would have to occur to enable a reopening of the embassy or, even harder, the drone base. In the meantime, the darkened embassy means no on-the-ground U.S. lines to those in power in Yemen. The closing of the drone base means a loss both of some U.S. intelligence gathering and of the capacity to kill purported U.S. enemies operating under al-Qaida or the Islamic State group.

If there is a lesson, it is that intimate U.S. involvement, with considerable dollars and personnel, in the politics of a country such as Yemen can come with some risk.