The USA had > 12 million men and women under arms at the end of WWII (7.6 million overseas). With increasing public demand for rapid demobilization, military personnel were returned to the U.S. on hundreds of transport ships and airplanes through Operation Magic Carpet.
The European phase of demobilization concluded in February 1946; the Pacific phase lasted until September 1946. By June 1947, the number of active duty personnel in the U.S. armed forces was reduced to 1,566,000.
The USA demobilized its military forces after the Civil War, WWI and WWII. Unfortunately, a retreat into isolationism, with the public reluctant to invest in the maintenance of a well-trained and equipped standing military force has resulted in significant losses for Americans in the early phases of past wars (e.g. Pearl Harbor and the invasion of South Korea).