From 1945 to 1951, MacArthur headed the allied occupation of Japan. MacArthur introduced major reforms in Japan's politically, economic, and social institutions. The Japanese respected his leadership. A new Japanese constitution went into effect in 1947. MacArthur also headed the U.S. far east command from 1947 to 1951.

MacArthur treated the  Japanese people very kindly, because he didn't want to interfere with their cultural lives. MacArthur had many goals that he wanted to achieve during his time in Japan. He did eventually achieve these goals after five years. One of the things that he wanted to achieve was, changing and revising Japan's constitution. He achieved this goal. MacArthur had to leave Japan in 1950 to fight in the Korean War.