The two dates most often mentioned as “the beginning of World War II” are July 7, 1937, when the “Marco Polo Bridge Incident” led to a prolonged war between Japan and China, and September 1, 1939, when Germany invaded Poland, which led Britain and France to declare war on Hitler’s Nazi state in retaliation.
In 1940, Japan joined the Axis. Japan wanted to expand its empire in Asia. In 1941, Japan destroyed U.S. Navy ships at Pearl Harbor. Thousands of Americans died.
The United States joined the Allied Powers. The Axis Powers declared war on the United States. Many Americans joined the military. Americans supported the war. They bought war bonds. Women worked in factories. Americans collected metal to make war supplies. Some Americans feared Japanese Americans would help Japan. The government forced thousands of Japanese Americans to live in internment camps.