World War II was a global conflict fought from 1 September 1939 to 2 September 1945. It began with Germany's invasion of Poland and eventually drew in nations from every part of the globe. The war pitted the Allied Powers (France, United Kingdom, USSR, United States, China and others) against the Axis Powers (Nazi Germany, Fascist Italy until 1943, and Imperial Japan).
It is the deadliest conflict in human history, with between 70 and 85 million deaths, the majority of them civilians. The war was marked by the Holocaust — the Nazi genocide of approximately 6 million Jews — and by the first use of atomic bombs, dropped on Hiroshima (6 August 1945) and Nagasaki (9 August 1945).
The post-war world was divided between the American and Soviet spheres of influence, beginning the Cold War.
The causes of World War II stem directly from the unresolved tensions of World War I. The harsh terms of the Treaty of Versailles (1919) humiliated Germany, fuelling resentment and nationalism. The Great Depression (from 1929) caused mass unemployment and drove people towards radical politics.
In Italy, Mussolini had seized power in 1922; in Germany, Adolf Hitler became Chancellor on 30 January 1933 and rapidly established a totalitarian regime. His expansionist programme — reuniting all German-speakers, conquering Lebensraum in the East, and eliminating Jews — set Europe on a path to war.
Western democracies pursued a policy of appeasement, allowing Hitler to remilitarise the Rhineland (1936), annex Austria (1938), and take the Sudetenland (Munich Agreement, 1938). The Molotov-Ribbentrop Pact (August 1939) freed Hitler from a two-front war. On 1 September 1939, Germany invaded Poland; France and Britain declared war on 3 September.
1939-1940 - Phoney War and Fall of France: After the rapid conquest of Poland (September 1939), a period of inactivity followed (the "Phoney War"). On 10 May 1940, Germany launched its Blitzkrieg through the Ardennes, bypassing the Maginot Line. France fell in six weeks; the armistice was signed on 22 June 1940. From London, General de Gaulle called for continued resistance.
1940 - Battle of Britain: Germany attempted to subdue Britain through aerial bombing (July-October 1940). The RAF's resistance forced Hitler to abandon his invasion plans.
1941 - War becomes global: On 22 June 1941, Germany launched Operation Barbarossa against the USSR. On 7 December 1941, Japan attacked Pearl Harbor; the United States entered the war the next day.
1942-1943 - Turning points: Allied victories at El-Alamein (October-November 1942) in North Africa and the German defeat at Stalingrad (surrendered February 1943) marked the turning of the tide.
1944-1945 - Liberation: The D-Day landings in Normandy (6 June 1944) opened a new western front. Germany surrendered on 8 May 1945. Atomic bombs on Hiroshima and Nagasaki in August 1945 led to Japan's surrender on 2 September 1945.
German Blitzkrieg bypassed the Maginot Line through the Ardennes. Allied forces were encircled. The Dunkirk evacuation (26 May - 4 June) rescued 338,000 Allied troops. France surrendered in 6 weeks.
One of the bloodiest battles of the war. The German 6th Army under Field Marshal Paulus was encircled by the Soviet Operation Uranus (November 1942). After 5 months of fighting in city ruins, Paulus surrendered with 91,000 survivors. This marked the decisive turning point on the Eastern Front.
British offensive by General Montgomery against Rommel's Axis forces (the "Desert Fox"). The Allied victory halted the Axis advance towards the Suez Canal and Egypt, marking the turning point of the North African campaign.
The largest amphibious operation in history (Operation Neptune/Overlord): 6,000 ships, 12,000 aircraft and 156,000 soldiers landed in Normandy under Supreme Commander Eisenhower. Operation Fortitude had deceived the Germans as to the landing location. Paris was liberated on 25 August 1944.
The United States dropped two atomic bombs on Japan: "Little Boy" on Hiroshima (6 August, ~140,000 deaths) and "Fat Man" on Nagasaki (9 August, ~70,000 deaths). These bombs, developed under the Manhattan Project, marked an absolute turning point in military history. Emperor Hirohito announced Japan's surrender on 15 August.
World War II was the deadliest conflict in human history, with 70 to 85 million deaths, the majority civilians. The USSR suffered the most (~26 million dead). The Holocaust — the systematic genocide of 6 million Jews by the Nazi regime — remains a defining moral reference in human history.
The war fundamentally reshaped the world order. Europe lost its global predominance; two superpowers emerged: the United States and the USSR. The post-war world was divided into two competing blocs, launching the Cold War (1947-1991). The United Nations was founded in 1945. Technologically, the war brought radar, jet aircraft, long-range missiles (V2) and the atomic bomb, inaugurating the nuclear age.