Ans/ The United States had refused to participate in the conflict. It did not want to confront all of the economic challenges that the First World War had produced. It couldn't, however, remain out of the battle for long. Japan was extending its influence to the east. It had taken over French Indo-China and was preparing to assault US naval bases in the Pacific. When Japan backed Hitler and struck the US base at Pearl Harbor, the United States entered the Second World War. The war concluded in May 1945, with Hitler's defeat and the United States firing an atomic bomb on Hiroshima, Japan.