Africa receives a small portion of Pentagon investment compared with Germany, South Korea and Japan, for instance.

General Waldhauser said Africa Command was the first to be asked to submit a drawdown plan, as The Times initially reported in June. But he said he expected other American combatant commands around the world to do the same under the defense strategy to better position the United States military against threats from Russia, China, Iran and North Korea.

The strategy represented a shift from fighting terrorism to countering state threats. When he announced it in January, Mr. Mattis declared that “we will continue to prosecute the campaign against terrorists, but great power competition — not terrorism — is now the primary focus of U.S. national security.”

The drawdown in Africa, General Waldhauser said, will include the departure of hundreds of Special Operations troops and their support forces. It will begin in places like Cameroon, where American war planners believe their efforts to train that country’s special operations forces have been largely successful. The United States currently has about 300 troops in Cameroon.

General Waldhauser said Cameroon’s security forces have improved to the point where they no longer need Americans to accompany them on missions.

“They can do it on their own,” he said. “That would be an example of a country where we have worked ourselves out of a job.”

A Defense Department official said that Nigerien forces are also considered to be improving to the point where they may soon not need American help.