The US entered the war in December 1941. Only in November 1943 was a psychiatrist added to the table of organization of each division, and this policy was not implemented in the Mediterranean Theater of Operations until March 1944. By 1943, the US Army was using the term "exhaustion" as the initial diagnosis of psychiatric cases, and the general principles of military psychiatry were being used. General Patton's slapping incident was in part the spur to institute forward treatment for the Italian invasion of September 1943. The importance of unit cohesion and membership of a group as a protective factor emerged.