During World War II, the United States got involved after Japan attacked Pearl Harbor in 1941. Before that, the U.S. tried to stay neutral but helped Britain with supplies through the Lend-Lease program. American industries increased production to support the war effort. The war started when Germany invaded Poland in 1939, followed by France and Britain joining in. The U.S. introduced a draft in 1939, and eventually joined the war against Germany, Japan, and Italy.