A global conflict involving the vast majority of the world's nations—including all of the great powers—organized into two opposing military alliances: the Allies and the Axis.
World War II was the deadliest conflict in human history, resulting in an estimated 70 to 85 million fatalities. Spanning across Europe, the Pacific, Atlantic, South-East Asia, China, Middle East, Mediterranean, and Africa, it reshaped the global political order and led to the creation of the United Nations and the onset of the Cold War.
Led primarily by the "Big Three":
Driven by expansionist authoritarian regimes:
The war began on September 1, 1939, when Germany invaded Poland, leading France and Britain to declare war. Utilizing Blitzkrieg tactics, Germany conquered France, Western Europe, and the Balkans by 1940. In June 1941, Germany invaded the USSR (Operation Barbarossa).
On December 7, 1941, Japan attacked the US naval base at Pearl Harbor, drawing the United States fully into the war. Critical turning points occurred in 1942–1943: the Battle of Midway in the Pacific, the Battle of Stalingrad in Eastern Europe, and Second El Alamein in North Africa.
The Allies invaded Italy in 1943 and launched the D-Day landings in Normandy on June 6, 1944. Following Allied advances on both fronts, Germany surrendered unconditionally on May 8, 1945 (V-E Day). Japan surrendered on September 2, 1945 (V-J Day) following the atomic bombings of Hiroshima and Nagasaki.