On December 7th, 1941, the Japanese navy, under the command of Admiral Isoroku Yamamoto, bombs Pearl Harbor. The same day, President Roosevelt declares war on Japan. Later, on December 11th, the United States declares war on Nazi Germany and Italy. The U.S. is finally in the war.
Later in the war, U.S. troops, along with British, ANZAC, and Canadian troops, land in Normandy. As we know, this leads to the demise of the Nazi regime and VE-day.