Meanwhile, Japan, who had already been at war with the Chinese since 1937, had launched a surprise attack on Pearl Harbor, leading the United States to join the Allied powers. In Europe, the Allies opened three fronts: in the west, after securing Normandy; in the east, aiding the Soviet Union; and in the south, through Italy. Germany eventually surrendered, upon which the Allies turned and focused troops to do island hopping. The dropping of the atom bombs on Hiroshima and Nagasaki led to the surrender of Japan and the end of the Second World War.
Worsening relationships between wartime Allies developed into the Cold War, reaching a climax during the Cuban Missile Crisis at the same time as the Sino-Indian War. Hostilities never actually occurred, though the US did kill in the communist states in the Korean War and the Vietnam War.