World War II

The Japanese attack on Pearl Harbor on December 7, 1941 ended two years of uneasy American neutrality in a single morning and pulled the United States into the largest war in human history. Over the next four years the country fought on two fronts at once — against Imperial Japan across the Pacific and against Nazi Germany and its allies in Europe — while converting its factories into an arsenal that out-produced every enemy combined.

In the Pacific, the United States clawed back ocean and island from Japan after the carrier victory at Midway in June 1942 turned the tide. In Europe, American forces joined the British and Soviets to squeeze Germany from all sides, a campaign that crested with the D-Day landings in Normandy in June 1944. Behind the front lines, industrial mobilization remade American society, drawing millions of women into the workforce and accelerating the migration that reshaped its cities.

The war ended in two stages and on a darker note than it began. Germany surrendered in May 1945; Japan fought on until the United States dropped atomic bombs on Hiroshima and Nagasaki that August, opening the nuclear age. Victory also carried a domestic shadow — the forced internment of 120,000 Japanese Americans, a wartime injustice the government would not formally apologize for until 1988.

World War II left the United States the strongest power on earth — its homeland untouched, its economy dominant, and its military reach global. It helped build the United Nations and a new international order, but the wartime alliance with the Soviet Union curdled almost immediately into the Cold War that would define the next half-century.