When does World War III start? Actually, it has already started. Before World War II, during the Spanish Civil War, the vast majority of countries believed the world was at peace. In 1931 and even 1937 when the Japanese invaded China, Western countries also had the perception that the world was generally peaceful. When the German Wehrmacht blitzkrieged Poland in 1939, the French still thought the world was at peace. It wasn't until June 1941 when Germany attacked the Soviet Union, and December when Japan attacked Pearl Harbor, that ordinary people in the Soviet Union and America felt that war had arrived.