WASHINGTON (AP) — Countering China's rapidly expanding military and an increasingly aggressive Russia are now the U.S. military's top national security priorities, outpacing the threat of terrorism, Defense Secretary Jim Mattis said Friday. He said competition with those adversaries has threatened America's military advantage around the world.

Laying out a broad new strategy for the Defense Department, Mattis warned that all aspects of the military's competitive warfighting edge have eroded.

He said building a force that can deter war with established and emerging military powers in Moscow and...