It was the biggest and deadliest war in history, spanning six grueling years and involving countries in nearly every part of the world. Sparked by the 1939 Nazi invasion of Poland, World War II pitted the Allied forces (led by the United States, Great Britain and the U.S.S.R.) against the Axis powers (Nazi Germany, Japan and Italy). Explore the battles, key players and atrocities from the war and its impact on geopolitics and humankind today. Featured Overview World War II History After the bombing of Pearl Harbor on December 7, 1941, President Franklin Roosevelt committed American forces to the Allied cause. Featured Overview World War II History After the bombing of Pearl Harbor on December 7, 1941, President Franklin Roosevelt committed American forces to the Allied cause. The majority of the world's countries eventually formed two opposing alliances: the Allies and the Axis. Why Did Japan Attack Pearl Harbor? By the time the first Japanese bomber appeared over Pearl Harbor on December 7, 1941, tensions between Japan and the United States had been mounting for the better part of a decade, making war seem inevitable. D-Day: Facts on the Epic 1944 Invasion That Changed the Course of WWII The Allied invasion of Normandy was among the largest military operations ever staged. The Holocaust was the persecution and murder of millions of Jews, Roma, political dissidents, homosexuals and others by the Nazi regime. The Hidden Army of Women That Helped Defeat Hitler Flashback: The Hidden Army of Women That Helped Defeat Hitler This 1944 American propaganda film imagine’s Hitler’s surrender and explains the Füher’s greatest mistake – his underestimation of American women. This episode of Flashback shows how female wartime workers were an indispensable part of America’s victory, even before the war was officially won. Battle of Britain (1940) This was the first battle in history fought solely in the air. For more than three months in 1940, pilots on both sides took to the skies and battled for control of airspace over Great Britain and the English Channel. Battle of Stalingrad (1942-1943) In a conflict that marked the war's outcome tipping in favor of the Allies, the Red Army defended the Russian city of Stalingrad from German attack, bringing an end to the Axis's eastern Europe advances. Iwo Jima (1945) Centered on a strategically important island 750 miles off the coast of Japan, this epic military campaign between U.S. Marines and Japan’s Imperial Army saw some of the bloodiest fighting of the war. Explore All Related Topics Francisco Franco Francisco Franco ruled Spain as a dictator from 1939 to 1975, rising to power in the Spanish Civil War and repressing political opponents. Pearl Harbor is a U.S. naval base in Hawaii that was attacked by Japan on December 7, 1941, leading the U.S. to enter World War II. These Photos Depict the 'Miracle of Dunkirk' That Saved 338,000 Lives

These photos show the chaos and courage of the 1940 evacuation, when hundreds of thousands of Allied troops escaped German forces by sea. 10 Photos From V-J Day Celebrations Around the World Victory over Japan Day ushered in peace after the devastation of World War II. The Atomic Bomb The atomic bomb and nuclear bombs, powerful weapons that use nuclear reactions as their source of explosive energy, were developed during World War II and are regulated by international agreements. What Were the Nuremberg Trials? The Nuremberg trials, which brought Nazi war criminals to justice, were carried out in Nuremberg, Germany, between 1945 and 1949. The Deadliest Ship Disaster in History Wasn’t the Titanic The torpedoing of the German ocean liner *Wilhelm Gustloff* in 1945 led to the deaths of some 9,000 men, women and children. The Secret World War II Plan That Used Astrology When conventional tactics fail, governments have been known to test the boundaries of reality. During the darkest days of World War II, Britain turned to an astrologer who claimed he could alter the course of the war using the power of the stars. How the WWII Burma Campaign Helped Turn the Tide Against Japan The grueling 1944–45 Allied offensive reopened the crucial overland supply route to China and dealt the Japanese army one of its worst defeats of the war. Molotov-Ribbentrop Pact The Molotov-Ribbentrop Pact was a non-aggression pact signed in 1939 by Nazi Germany and the Soviet Union before World War II broke out. The pact lasted until Hitler invaded the Soviet Union in 1941. The US Home Front During World War II On the home front during World War II, life in the U.S. was changed by rationing, defense production, women’s jobs and popular radio and movie entertainment. Rosie the Riveter Rosie the Riveter was the star of a campaign aimed at recruiting female workers for defense industries during World War II. Artist Normal Rockwell's cover image of Rosie, made in 1943, became, perhaps the most iconic image of working women. The Dawn of the Nuclear Age The end of the Second World War and the dawn of the nuclear age saw its two great victors go from allies to adversaries. The Atomic Bomb Changes the Course of the War The most terrible weapon ever created changes the course of the war in the Pacific. Hiroshima, Then Nagasaki: Why the US Deployed the Second A-Bomb The explicit reason was to swiftly end the war with Japan. But it was also intended to send a message to the Soviets. Why Route 66 Played a Critical Role During World War II Troops and military supplies traversed the Mother Road throughout the early 1940s.