The Lend-Lease act was passed by Congress on this day and allowed the sale or lease of weapons and supplies to any country that was struggling against the Axis powers, provided the President deems it vital to the US defense. This officially eliminated any neutrality that the US had shown earlier in the war. Additionally, it allowed the US to react faster to the Japanese bombing of Pearl Harbor because they were already building up their defense.
The Japanese bombing of Pearl Harbor was unexpected due to the US not having declared war on any country. However, this event immediately entered the US into war, not only with Japan, but into the European war. Additionally, it led to Executive Order 9066, or the relocation of Japanese-Americans to internment camps. Overall, the attack on Pearl Harbor led to the US fighting World War II on an additional front; the one in the Pacific.
The Battle of Midway, lasting 4 days from June 4th to June 7th, was a decisive naval win for the US near the Midway Atoll in the Pacific. US Navy Admirals Chester Nimitz, Frank Jack Fletcher, and Raymond A. Spruance led the attack that damaged the Japanese naval fleet beyond repair, turning the tide in the Pacific Theater of the war.
The D-Day Invasion of the Normandy beaches allowed the Allied Powers to get a foothold in the Axis dominated France. US General Dwight D. Eisenhower oversaw the invasion, named Operation Overload. This invasion allowed the Allied Powers to land more troops on the ground in France, making it easier to push back on Germany.
The First successful test of the Atomic Bomb, part of the Manhattan Project, took place in Alamogordo, New Mexico. Robert J. Oppenheimer directed the project at its facility in New Mexico and was one of the first people to watch the bomb detonate. The bomb was originally intended for use on the Germans, but was then used as a threat to the Japanese. When the Japanese did not surrender, it was used. Additionally, President Truman took a firmer stance against Stalin when discussing post war Europe, and soon afterwards, in 1949, the Soviet Union had developed their own atomic bomb, and the Cold War began.
The formal Japanese surrender to the US on September 2nd represents the official end of World War II. The ceremony took place in Tokyo Bay, Japan, aboard the battleship USS Missouri, and was signed by representatives of the Japanese empire, as well as many representatives of the Allied powers including Fleet Admiral Chester Nimitz for the United States.