World War II: History of the Global Conflict 1939-1945

The Second World War, WWII, and WW2 redirect here. For other uses, see The Second World War and WWII.

World War II: A Global Conflict (1939–1945)

World War II, also known as the Second World War, was a global war that lasted from 1939 to 1945. The vast majority of the world's countries—including all the great powers—eventually formed two opposing military alliances: the Allies and the Axis.

Total War and the Deadliest Conflict in History

A state of total war emerged, directly involving more than 100 million people from more than 30 countries. The major participants threw their entire economic, industrial, and scientific capabilities behind the war effort, blurring the distinction between civilian and military resources. World War II was the deadliest conflict in human history, marked by 70 to 85 million fatalities, most of whom were civilians in the Soviet Union and China. It included massacres, the genocide of the Holocaust, strategic bombing, premeditated death from starvation and disease, and the only use of nuclear weapons in war.

The Outbreak of War in Europe and Asia

Japan, which aimed to dominate Asia and the Pacific, was at war with China by 1937, though neither side had declared war on the other. World War II is generally said to have begun on 1 September 1939, with the invasion of Poland by Germany and subsequent declarations of war on Germany by France and the United Kingdom.

Axis Expansion and the Molotov–Ribbentrop Pact

From late 1939 to early 1941, in a series of campaigns and treaties, Germany conquered or controlled much of continental Europe and formed the Axis alliance with Italy and Japan. Under the Molotov–Ribbentrop Pact of August 1939, Germany and the Soviet Union partitioned and annexed territories of their European neighbors: Poland, Finland, Romania, and the Baltic states. Following the onset of campaigns in North Africa and East Africa, and the Fall of France in mid-1940, the war continued primarily between the European Axis powers and the British Empire. War in the Balkans, the aerial Battle of Britain, the Blitz, and the long Battle of the Atlantic followed.

The Eastern Front and the War in the Pacific

On 22 June 1941, the European Axis powers launched an invasion of the Soviet Union, opening the largest land theater of war in history. This Eastern Front trapped the Axis, most crucially the German Wehrmacht, in a war of attrition. In December 1941, Japan launched a surprise attack on the United States as well as European colonies in the Pacific. Following an immediate U.S. declaration of war against Japan, supported by one from Great Britain, the European Axis powers quickly declared war on the U.S. in solidarity with their Japanese ally. Rapid Japanese conquests over much of the Western Pacific ensued, perceived by many in Asia as liberation from Western dominance and resulting in the support of several armies from defeated territories.

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