On December 8, 1941 President Franklin Roosevelt declared war on the Japanese. That day he gave the " Day of infamy speech' he declared shortly after the bombing of pearl harbor.
All the Japanese people who lived in the u.s were all taken away during the war, the u.s feared that would stay loyal to their ancestral land they were moved and forced to shut down their bussiness stores and sell homes.
During the war, The u.s made some internment camps for the japanese people who were living in the u.s because they thought they were spies and were just scared that they would do something to help the japanese with the war.
The u.s want the japanese to surrender and they refuse to do so, The u.s start to plan a huge attack on japan which would make them. They wanted to invade japan but were scared to do so.
The u.s creates an atomic bomb that is very powerful and they know it will wipe out a lot of people, they were the first country to develop it. They go out to the desert to test it and saw how powerful and dangerous this can be.
On August 6, 1945 the U.S dropped the first ever atomic bomb on japan, it was dropped on hiroshima about two-thirds of the city was destroyed immediately and about 66,000 people were killed. 3 days later they dropped another one on Nagaski and half of the city was wiped killing 39,000 people.