Japan needed to get trough the Pacific with ease so that their plans of an invasion of North America would be successful. The only thing that stood in their way was Pearl Harbor (owned by the United States). Pearl Harbor was attacked by the Japanese Imperial Navy, at approximately 8:00 A.M., Sunday morning, December 7, 1941. 353 Japanese aircraft had been in this assault and no declaration of war had been stated at this time. Therefore the United States were not ready for this attack. Approximately 100 ships of the U.S. Navy were present that morning, consisting of battleships, destroyers, cruisers and various support ships. Over half the U.S. Pacific fleet was out to sea, including the carriers. A total of twenty-nine Japanese aircraft were shot down by ground fire and U.S pilots from various military battalions. This attack on Pearl Harbor was the incentive for the United States to join the war.
With them joining it gave the allies enough fresh troops to defeat Germany and Japan.
The atomic Bomb was completed by Albert Einstein in 1944 and cost the United States over $2 billion. Nick named that Manhattan project, and was top secret. The A-bomb as it is also known as was one of the smallest bombs but did the most destruction ever. You would be able to take out an entire town with one A-bomb. Everyone during WWII was trying to develop this weapon because they knew if they did the country to do so would probably win the war. Allied troops found German factories with A-bomb plans in them. The Germans probably didn't have enough resources, like uranium, to complete this project and that is why they fell short. The United States completed their bomb first because of Canada's supply of uranium.