The United States tried to stay out of World War II as long as possible. For a few years they just aided British and other allies during the war. The United States had control over Japan’s oil and that was the only thing that could set Japan back.
The United States delayed cutting Japan’s oil supply off in fear of attack or attack on allies. However, in 1941 Japan entered Indonesia. After Japan occupied Indonesia the United States cut off all oil and assets to Japan. Japan for infuriated and was planning to seek revenge.
On December 7, 1941 while the United States government was in a meeting with Japan’s representatives trying to come up with some agreement, Japan launched a surprise attack on the naval base Pearl Harbor in Hawaii. The United States never saw the attack coming. Many ships and airplanes were destroyed. The United States’ ability to win a war in the Pacific would be a very little chance with their naval base destroyed. One day after the attack United States and Britain declared war on Japan. Germany and Italy declared war three days later on the United States.
When the Japanese kept refusing to surrender the Americans decided it was time to take things into their own hands. The American army was still small and inexperienced so they let the scientific study of atomic energy take over. In August 1945 the Americans dropped an atomic bomb on Hiroshima and two days later on Nagasaki. The war ended with a treaty in September 1945.
It is still a question today if the atomic bombs were needed to end the war. Some people may not understand that one of the reasons the Americans used to atomic bomb was to scare the Russians so they would trust their allies. But what the Americans did know was the atomic bomb would put an immediate stop on the war.