From 1926 to 1928, Richardson was military attaché in Rome, Italy. He also studied at the General Staff School, the École Supérieure de la Guerre in Paris, and the Army War College, and from 1929 to 1933, he was commandant of cadets at West Point. Promoted to brigadier general in June 1938, Richardson commanded the 2nd Cavalry Brigade at Fort Bliss, Texas, in 1938 and 1939 and, also at Fort Bliss, the 1st Cavalry Division in 1939 and 1940. After becoming a major general in October 1940, he was director of the War Department's Bureau of Public Relations from February to August 1941.
From 1941 to 1943, Richardson commanded VII Corps in the United States, where he trained troops. In mid-1942, as Army Chief of Staff General George C. Marshall's personal representative, he made a tour of inspection of the Pacific area. In June 1943, he was promoted to lieutenant general and became military governor of the Hawaiian Department, where he recommended a major military reorganization in the Pacific; when it was implemented in August 1943, Richardson became commanding general of U.S. Army forces in the Pacific Ocean Area, including the Hawaiian Department.
Richardson had no operational responsibilities, but from then until the end of the war, he trained troops and helped plan all the major Pacific campaigns. Unlike General Douglas MacArthur, commander in chief of the Southwest Pacific Theater, Richardson enjoyed good relations with Admiral Chester W. Nimitz, commander in chief of the Pacific Ocean Area, and also with George C. Marshall, the army's chief of staff. Richardson retired from the army in September 1946. He died in Upper Village, Bath, New Hampshire, on 2 March 1954. He was promoted posthumously to full general.
Coakley, Robert W., and Richard M. Leighton. Global Logistics and Strategy, 1940–1945. 2 vols. Washington, DC: U.S. Government Printing Office, 1955, 1968.; Matloff, Maurice. Strategic Planning for Coalition Warfare, 1943–1944. Washington, DC: U.S. Government Printing Office, 1959.; Miller, Edward. War Plan Orange: The U.S. Strategy to Defeat Japan, 1939–1945. Chapel Hill: University of North Carolina Press, 1991.; Morton, Louis. Strategy and Command: The First Two Years. Washington, DC: U.S. Government Printing Office, 1962.