World War II did not begin with the bombing of Pearl Harbor. That attack culminated a long period of tension in the United States caused by Japanese, Italian, and German aggression. Despite that tension—and despite the fact that much of the world had been at war since 1939—when the Japanese attacked, they found Americans both militarily and psychologically unprepared. Pearl Harbor shocked Americans into a war they previously had been reluctant to fight.

The United States in a Troubled World

The causes of World War II extended back to the peace talks at Versailles that ended World War I. Issues that divided victors and vanquished then, such as German reparations and the naval arms race, continued to trouble international relations for another 25 years. Despite its economic power, the United States played only an indirect role in the postwar world. The most direct threat to the peace during the 1920s arose from Japan's aspirations in Manchuria. The United States proposed little in opposition to this aggression aside from the Stimson Doctrine of nonrecognition of Japan's conquests. In Latin America, the United States under Hoover and Roosevelt took some constructive steps to become a "Good Neighbor," although that did not lessen in any way American dominance of the region's economies.

Franklin Roosevelt was one of the most internationally-minded American presidents. Yet domestic pressures against foreign political entanglements left him largely powerless to play a role in containing the spread of German and Italian fascism or Japanese militarism. Neutrality legislation limited FDR's power to support victims of aggression such as Ethiopia and China. That impotence made him sympathetic to the efforts of French and English leaders, who at Munich in 1938 sought to negotiate an end to Hitler's aggression in Europe. Munich proved a sellout of Czechoslovakia, however, rather than a diplomatic triumph. With the German invasion of Poland in 1939, Europe once again plunged into war. Determined to play a decisive role in the European theater, Roosevelt tried to avoid a showdown in the Pacific with Japan, but diplomatic talks produced no compromises. Meanwhile, the Japanese extended their empire and began secretly planning an attack on the American naval base at Pearl Harbor.

A Global War

When the United States entered the war, it suffered a string of demoralizing defeats. But the key to victory became the productive capacity of American factories and the ability of the Americans and their Russian and British allies to coordinate a strategy, first to defeat Germany and only then to concentrate on defeating Japan. In Roosevelt, Churchill, and Stalin, the Allies had exceptional leadership.

Despite agreement to defeat Germany first, the Allies' first successes came in naval engagements in the Pacific, highlighted by a smashing victory at Midway. After the Anglo-American invasion of North Africa, victories at El Alamein and Stalingrad in late 1942 marked the turning point of the war with Germany. By then American factories were operating at full production and the armed forces were prepared to battle the enemy on all fronts.

The war mobilized not just soldiers, but also women and minorities. All of them made unprecedented contributions. Many young men and women found themselves far from home for the first time. For African Americans, service offered an unusual opportunity for education and decent living conditions. They volunteered in great numbers. Unfortunately, the prejudices of civilian life often extended into interracial tensions in the military. Gay Americans had a similar experience. They too had new opportunities and encountered widespread prejudices. Women were a third group who showed their patriotism by joining the services. While they achieved equal status in some ways, they were often restricted socially and allowed only a limited role.

War Production

Before the United States entered the war, President Roosevelt spoke of the nation as "the arsenal of democracy." But after the government eliminated the initial bottlenecks, a pattern emerged. Shortages led to the search for explanations and solutions. Industries developed new techniques or new products that ended the shortages. In the long run, organization for war increased the consolidation of key industries into fewer, but larger, corporations. Scientists made critical contributions—such as radar and the proximity fuse—that may have proven decisive on the battlefield, but they too introduced new technologies that had important peacetime applications. The fear of German advances in fission research prompted Roosevelt to authorize the Manhattan Project. American scientists raced the Germans to chain the power of the atom to a weapon of war.

War production brought back prosperity but also created headaches as Americans adjusted to shortages and dislocations (the latter becoming a particular problem for laborers not just in the United States but around the world). In all facets of the war economy, the Roosevelt administration tried to achieve its results through voluntary means, such as the sale of war bonds. It resorted to compulsion only when necessary, as when it increased taxes to finance the war. Issues such as what taxes ought to be levied divided liberals and conservatives.

Labor unions generally cooperated in keeping industry functioning smoothly, but a few militant leaders such as John L. Lewis insisted on winning major concessions even if it hurt war production. Labor shortages increased the demand for women workers. These laborers included not only the traditional young and single women, but also married women with children. The need for income, new opportunities, and a sense of patriotism all attracted women to jobs, but they found that many of the old barriers to advancement remained.

A Question of Rights

World War I had resulted in severe infringements of civil rights. The United States had a better record during World War II, but significant violations continued to occur. German and Italian aliens faced restrictions for less than a year, but Japanese Americans suffered a harsher fate as the government, in response to hysteria and bigotry, herded them into concentration camps. Even the Supreme Court gave its blessing to this injustice.

At the same time, traditional forms of prejudice limited the opportunities of African Americans and Hispanics. Black leader A. Phillip Randolph pressured Roosevelt into creating the Fair Employment Practices Commission, which in some cases was able to end job discrimination. The movement of minorities into industrial centers outside the South often created friction, which in Detroit, New York, and Los Angeles erupted into violence. Despite limited gains during the war, minority leaders had laid the groundwork for future activism.

Though the war had bipartisan support, partisan politics continued. The foes of New Deal reform used the war as an excuse to end programs they opposed. Still, Roosevelt managed to win an unprecedented fourth victory over Thomas Dewey in the 1944 presidential election. To satisfy conservative Democrats, he chose Harry Truman of Missouri as his vice-president.

Winning the War and the Peace

Winning the war required a coordinated military and diplomatic strategy in Europe and the Pacific. The Allies first drove Italy from the war before Anglo-American forces stormed the beaches of Normandy on D-Day, June 6, 1944. After a ferocious German counterattack failed during the Battle of the Bulge, the Allies marched toward Berlin. By then, the forces of General MacArthur and Admiral Nimitz had moved within bomber range of Japan. The Axis faced certain defeat, though a bloody struggle remained ahead. In both theaters of the war the massed attacks of long-range bombers showed how air power had eliminated the concept of the front lines from war.

At a series of wartime meetings, Roosevelt, Churchill, and Stalin met to plan a global strategy and lay the grounds for the postwar peace. They disagreed on many key points, including the best way to preserve peace. Still, they managed to compromise their differences in the interests of the war effort. The high point of cooperation came at Teheran in 1943, when the three leaders agreed to the D-Day invasion of Europe. By the time they met at Yalta in February 1945, Roosevelt had secured a Soviet pledge to enter the war against Japan, but serious divisions had arisen over Poland and Germany.

Yalta marked the final and most controversial episode of Roosevelt's diplomatic stewardship. Critics later charged that he had sold out American and Allied interests to the Communists; defenders recognized Roosevelt's concessions to Stalin on Poland, eastern Europe, and Asia as unavoidable, given the Soviet Union's wartime sacrifices and successes. Having led the Allies skillfully, Roosevelt neither enjoyed the fruits of victory nor suffered the failures of the peace, for he died weeks before the German surrender. The task of bringing the war to an end and the peace to fruition fell to Harry Truman.

Victory brought a series of shocks. In liberating Germany and Poland, Allied armies confronted the grisly evidence of the Holocaust. Hitler had ordered the systematic extermination of Europe's Jews and other groups stigmatized by Nazi ideology. A combination of anti-Semitism and economic fears had blocked any steps by the United States to ease the plight of the Jews. Only as the war neared its end did the government establish the War Refugee Board to assist European Jews.

The responsibility of bringing the United Nations and new international economic institutions into existence fell to Truman, as did managing relations—which grew ever more troubled—with the Soviet Union. Truman spent two weeks meeting with the British and Russians at Potsdam in Germany without resolving any important issues of the peace, such as German reparations. Even more consequential for postwar affairs, the first successful test of an atomic bomb led to its use on two Japanese cities. The horror of those attacks brought the war swiftly to an end, although controversy persisted over whether the United States actually needed to use such a weapon. "World War II changed everything," an admiral remarked. It especially promoted bigness and consolidation in government, business, and agriculture. Also, it made the United States the world's greatest power, with a monopoly on the world's most awesome weapon.