When former Army Captain and U.S. Senator Harry S Truman became the Commander in Chief, the United States military had organized, trained and equipped 89 ground divisions (67 infantry, 16 armored, five airborne and one mountain) and a number of independent regimental combat teams.1 In late 1945 the Army began to reorganize for new missions, which included occupying former enemy territories and establishing a General Reserve, while demobilizing the majority of the World War II forces. Within a year after the end of the war in Europe, the total number of divisions on active duty had decreased from 89 to 16; of these, 12 were engaged in occupation duty and the remaining four were in the United States.By the end of January 1947 three more infantry divisions overseas were inactivated and the 3d Infantry Division was withdrawn from Germany and sent to Camp (later Fort) Campbell, Kentucky, where it replaced the 5th Infantry Division. When demobilization ended in 1947, the number of active divisions stood at 12.While the Army developed and reorganized its postwar divisions, it continued to maintain and redeploy its existing forces to meet changing international situations. With the ratification of the Italian peace treaty in the fall of 1947, the Army inactivated the 88th Infantry Division (less one infantry regiment, which remained in Trieste) and at the end of 1948 withdrew its forces from Korea.2 To make room in Japan for the 7th Infantry Division, the 11th Airborne Division, which had been stationed there since 1945, redeployed to Fort Campbell, where it was reorganized with only two of its three regimental combat teams. The reduction of forces in Korea also resulted in the inactivation of the 6th Infantry Division. Four years after the end of World War II the number of Regular Army divisions had been reduced to 10 and were deployed around the world. The 52 Organized Reserve Corps and National Guard divisions were at various levels of readiness.Initially overwhelmed by the tidal wave of demobilization after World War II, the Army had struggled to rebuild both Regular Army and reserve divisions during the late 1940s. Its divisional structures were based on combat experiences during the war, under the assumption that atomic weapons would not alter the nature of ground combat. Units previously attached to divisions from higher headquarters during 2 combat were made organic to divisions, which also received additional firepower. The postwar divisions of the era were not fully prepared for combat because they were not properly manned and equipped; they nonetheless represented an unprecedented peacetime force in the Army of the United States, reflecting the new Soviet-American tensions.When a Soviet-trained and -armed North Korean army attacked South Korea in June 1950, the Cold War turned hot. The U.S. Army was forced to adopt emergency expedients during the first months of the war; the retention of a significant military sustaining base after World War II allowed the nation to mobilize. Within a year and a half the number of Army combat divisions on active duty went from 10 to 20. The Army, reacting to changing political, strategic and operational requirements worldwide, for the first time in its history reassessed its reserve forces during a major war. Nevertheless, the end of the fighting in Korea brought new reductions, which resulted in fewer Army divisions by the end of the decade than during the war.