On August 10, 1949, amendments to earlier legislation consolidated the U.S. military services under a single Department of Defense. The change followed lessons from World War II, where coordination among the services had been essential. The new department replaced the earlier National Military Establishment and strengthened the authority of the secretary of defense. It brought the Army, Navy, and newly independent Air Force under one umbrella. The structure allowed for more unified planning and budgeting. The department remains a central institution in national security policy.
