Prior to the attack on Pearl Harbor, the US had maintained a policy of neutrality, staying out of the war. Even though the US stayed out of the war, the US was still supplying weapons and aiding the Allied forces without direct involvement in the war. However, after the attack on Pearl Harbor by Japan, the US stepped in and declared war on Japan and stepped in. The US joining was a major turning point for the war, as the U.S. rapidly mobilized its industrial and military resources, becoming a major power, or “MVP :D.” Now this was December of 1941 when the U.S. stepped in. After 4 years, on September 1945, the war came to an end after the U.S. dropped two atomic bombs on Hiroshima and Nagasaki, where Japan surrendered.