World War II began in 1939 with the German invasion of Poland. By 1940, Paris had fallen to the Nazis and the US entered the war after the Japanese bombing of Pearl Harbor in 1941. The war ended in 1945 after the US dropped atomic bombs on Hiroshima and Nagasaki. Europe lay in ruins as Russia and the US emerged as rival superpowers in the postwar period. The Holocaust was revealed, with over 6 million Jews killed by the Nazis and horrifying conditions discovered at camps like Bergen-Belsen and Buchenwald. Artists struggled to represent the trauma of the war, with many turning to abstract styles to depict the indescribable.