The United States entered World War II following the surprise attack on Pearl Harbor by Japan on December 7, 1941. The next day, President Franklin D. Roosevelt formally declared war on Japan. Subsequently, Germany and Italy declared war on the United States, drawing the nation into a broad conflict that spanned several continents and profoundly altered its trajectory.

Domestically, the war spurred a dramatic transformation of the U.S. economy. Military production replaced consumer manufacturing, with factories shifting to the mass production of planes, tanks, ships, and weapons. This industrial mobilization helped to end the lingering economic hardships of the Great Depression and generated millions of new jobs. More women joined the workforce than ever before, symbolized by the iconic figure “Rosie the Riveter,” while minority communities also found increased employment opportunities despite ongoing discrimination.

American military forces were significantly engaged in both the European and Pacific theaters of war. In Europe, U.S. troops participated alongside Allied forces in key operations across North Africa and Italy. The campaign culminated in the D-Day invasion of Nazi-occupied France on June 6, 1944, a pivotal event that helped pave the way for the defeat of Nazi Germany in May 1945.

In the Pacific theater, American forces carried out a strenuous island-hopping campaign against Japan. Important battles at Midway, Iwo Jima, and Okinawa gradually brought U.S. troops closer to Japan’s home islands. The war in the Pacific concluded after the United States dropped atomic bombs on Hiroshima and Nagasaki in August 1945, which led to Japan’s surrender and the end of the conflict.

The war also had significant repercussions within the United States. The forced internment of Japanese Americans during the conflict remains a subject of substantial controversy and regret. Meanwhile, veterans returning from service contributed to the momentum of the civil rights movement by advocating for greater social and political equality across the country.

By the end of World War II, the United States had solidified its status as a leading global superpower. It played a central role in the creation of international institutions such as the United Nations and was instrumental in shaping the postwar global order. The war not only secured military victory abroad but also set in motion lasting changes in American society, the economy, and its position on the world stage.