Complex sentence: In May 1945, after the German surrender, Hodges and his troops were ordered to prepare for the invasion of Japan; that became unnecessary, however, when the atomic bomb and the declaration of war by the Soviet Union caused Japan's surrender later that year.
Split into simpler sentences: In May 1945, after the German surrender, Hodges and his troops were ordered to prepare for the invasion of Japan. That became unnecessary, however, when the atomic bomb and the declaration of war by the Soviet Union caused Japan's surrender later that year.