Beginning in Europe in 1939, World War II was fought between the Axis (Germany, Japan and Italy) and the Allies (the United States, Great Britain and the Soviet Union). The United States remained neutral for the first two years of conflict, but was forced to enter in response to the Japanese attack on the American fleet at Pearl Harbor on Dec. 7, 1941.
In the beginning, the United States was allied with Great Britain and France, two countries already involved in the war. President Roosevelt provided these allies with arms to support their fight against Germany, and this support increased after France was invaded in June 1940. Roosevelt passed the Lend-Lease Act in March 1941, which allowed for the direct lending, leasing, selling and bartering for arms between Great Britain and the United States.
After the bombing of Pearl Harbor, the U.S. Congress voted to declare war. Shortly after this decision, Adolf Hitler declared war on the United States. The United States' entry into World War II became a major turning point that led to victories for the Allies at the Battle of Midway (1942); the invasion of Italy (1943); the Allied invasion of France (1944); and the eventual surrender of the Axis powers in 1945.