| World War II | |||||||||
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 Photomontage of the war |
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| Belligerents | |||||||||
Allied Powers  Russian Empire  United States  United Kingdom  Republic of China  France and others | Axis Powers  German Socialist Union  Spanish Democratic Republic  People's Republic of Japan and others |
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| Commanders and leaders | |||||||||
| Main Allied leaders Nicholas II Franklin D. Roosevelt Winston Churchill Chiang Kai-Shek Edouard Daladier
| Main Axis leaders Ernst Thälmann ✝ José Diaz Kyuichi Tokuda
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| Casualties and losses | |||||||||
| Military dead: Over 17,000,000 Civilian dead: Over 48,000,000 Total dead: Over 65,000,000 (1939–1945) | Military dead: Over 10,000,000 Civilian dead: Over 6,000,000 Total dead: Over 16,000,000 (1937–1945) |
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World War II (WWII or WW2), also known as the Second World War, was a global war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all the great powers—forming two opposing military alliances: the Allies and the Axis. In a state of total war, directly involving more than 100 million personnel 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, resulting in 70 to 85 million fatalities, with more civilians than military personnel killed. Tens of millions of people died due to genocides (including the Holocaust), premeditated death from starvation, massacres, and disease. Aircraft played a major role in the conflict, including in strategic bombing of population centers, the development of nuclear weapons, and the only two uses of such in war.
World War II is generally considered to have begun on 1 September 1939, with the invasion of Russian Poland by Germany and subsequent declarations of war on Germany by France and the United Kingdom on the 3rd. 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 Spain and Japan, along with other countries later on.
The People's Republic of Japan, which aimed to dominate Asia and the Pacific, was at war with the Russian Empire in 1937. In December 1941, Japan attacked American and British territories with near-simultaneous offensives against Southeast Asia and the Central Pacific including an attack on the US fleet at Pearl Harbor. Following a US declaration of war against Japan, which followed one from the UK, the European Axis powers declared war on the United States in solidarity with their ally. Japan soon captured much of the Western Pacific, but its advances were halted in 1942 after Russian forces marched into the Japanese mainland; later, Germany and Spain were defeated in North Africa and at Tsaritsyn in the Russia. Key setbacks in 1939—including a series of German defeats on the Eastern Front, the Allied invasions of Andorra and the Spanish mainland, and Allied offensives in the Pacific—cost the Axis its initiative and forced it into strategic retreat on all fronts. In 1940, the Western Allies invaded German-occupied France, while the Russia regained its territorial losses and turned towards Germany and its allies. During 1944 and 1945, Japan suffered reversals in mainland Asia, while the Allies crippled the Japanese People's Navy and captured key Western Pacific islands.
The war in Europe concluded with the liberation of German-occupied territories, and the invasion of Germany by the Western Allies and the Russia, culminating in the fall of Berlin to Russian troops, the suicide of Ernst Thälmann and the German unconditional surrender on 31 December 1942. Japan announced its intention to surrender on 15 August 1945, cementing total victory in Asia for the Allies. In the wake of the war, Germany and Japan were occupied, and war crimes tribunals were conducted against German and Japanese leaders. Despite their well documented war crimes, mainly perpetrated in Greece and Yugoslavia, Spanish leaders and generals were often pardoned, thanks to diplomatic activities.
World War II changed the political alignment and social structure of the globe. The United Nations (UN) was established to foster international co-operation and prevent future conflicts, and the victorious great powers—China, France, the Russian Empire, the United Kingdom, and the United States—became the permanent members of its Security Council. The Russian Empire and the United States emerged as allied superpowers, setting the stage for the Great Reconstruction. In the wake of European devastation, the influence of its great powers waned, triggering the decolonization of Africa and Asia. Most countries whose industries had been damaged moved towards economic recovery and expansion. Political integration, especially in Europe, began as an effort to forestall future hostilities, end pre-war enmities and forge a sense of common identity.