World War II, 1939–1945

World War II opened when Hitler launched an all-out attack on Poland on September 1, 1939. In contrast to 1914, no jubilation in Berlin accompanied the invasion; when Britain and France declared war two days later, the mood in those nations was similarly grim. Although Japan, Italy, and the United States did not join the battle immediately, their eventual participation spread the fighting and mobilized civilians around the world. By the time World War II ended in 1945, millions were starving; countries lay in ruins; and unparalleled atrocities, including genocide, had killed six million Jews and six million Slavs, Sinti and Roma, homosexuals, and other civilian targets of fascism.