Soon after World War II ended, the uneasy alliance between the United States and the Soviet Union began to degenerate, and a long-standing ideological and military confrontation between the two superpowers quickly set in. By late 1946, the Truman administration had adopted a defense policy that became known as containment. This policy sought to contain Soviet influence and the spread of communism throughout the world. It was this mind-set that prompted passage of the National Security Act.
By the end of 1947, the containment policy had elicited both the enunciation of the Truman Doctrine and the implementation of the Marshall Plan. The National Security Act was an effort to add a domestic component to containment and to help coordinate U.S. diplomatic and military commitments to meet the challenges of the Cold War. The act was designed to centralize the military services under the single banner of the DOD—which was directed by the secretary of defense, a new cabinet-level position—to provide one main intelligence apparatus in the new CIA and to provide foreign policy advice directly to the president via the NSC, which resided within the Executive Office of the president. The JCS, composed of a representative from each of the armed services, was to act as a military advisory group to the president and his civilian advisors.
The CIA emerged from the World War II Office of Strategic Services (OSS) and smaller postwar intelligence operations. Its first director was Rear Admiral Roscoe Hillenkoetter. The existing War and Navy Departments were folded into the DOD, whose first secretary was James V. Forrestal. The new U.S. Air Force, which became a free-standing entity, was built from the existing U.S. Army Air Corps. The NSC's chief role was to coordinate and prioritize information it received from other agencies and to advise the president on national security issues based on analysis of that information. At the time, there was no provision made for a national security advisor, a post that came into being under President Dwight D. Eisenhower in 1953. Taken in its totality, the National Security Act provided for a powerful, well-coordinated system that linked national security with foreign policy and military decision making.
Leffler, Melvyn P. A Preponderance of Power: National Security, the Truman Administration, and the Cold War. Stanford, CA: Stanford University Press, 1992.; U.S. Department of State. Foreign Relations of the United States, 1945–1950: Emergence of the Intelligence Establishment. Washington, DC: U.S. Government Printing Office, 1996.