In 1947, Congress passed the National Security Act, which created the CIA, the Defense Intelligence Agency, and created the framework for a permanent, globe-spanning military establishment under the aegis of what was now called the Department of Defense. Five years later, the National Security Agency, which originated as the US Army's Cipher Bureau and Military Intelligence Branch in World War I, was given institutional permanence as well.

These initiatives grew out of the open-ended Cold War conflict with the Soviet Union, which was described of a crisis of sufficient magnitude to justify putting the United States on a permanent war footing.

Speaking on behalf of the Founding Generation, James Madison had advised that "no nation could preserve its [liberty] in the midst of perpetual warfare," which would strengthen the executive branch and undermine restraints on government power. Madison's warning would be ironically validated by his own actions during the War of 1812.