Answer:
The military history of the United States in World War II covers the war against the Axis Powers, starting with the 7 December 1941 attack on Pearl Harbor. During the first two years of World War II, the United States had maintained formal neutrality as made official in the Quarantine Speech delivered by US President Franklin D. Roosevelt in 1937, while supplying Britain, the Soviet Union, and China with war material through the Lend-Lease Act which was signed into law on 11 March 1941, as well as deploying the US military to replace the British forces stationed in Iceland. Following the "Greer incident" Roosevelt publicly confirmed the "shoot on sight" order on 11 September 1941, effectively declaring naval war on Germany and Italy in the Battle of the Atlantic.[1] In the Pacific Theater, there was unofficial early US combat activity such as the Flying Tigers.