Following the war, he was assigned as an instructor to the Army's School of Intelligence in Fort Leavenworth, Kansas.
Starting in 1948 and continuing throughout the Korean War, Davidson was chief, Plans and Estimates Branch, in General Douglas MacArthur's intelligence office. It was during this time that occurred one of the US Army's greatest intelligence failures in history - not predicting Chinese intervention in the Korean War.
During the Vietnam War, 1967 until 1969, Davidson was the chief of US military intelligence in Vietnam, under the command of William Westmoreland and later Creighton Abrams. From May 3, 1971, to September 30, 1972, Davidson, then a major general, was the Assistant Chief of Staff for Intelligence, Headquarters, Department of the Army. He was later promoted to lieutenant general.[2]
In 1988, he published Vietnam at War: The History 1946–1975,[3] which is widely regarded as one of the most comprehensive accounts of the Indochina wars.[4] He followed it up in 1990 with Secrets of the Vietnam War,[5] where he described his experiences in Vietnam.