Second World War

World War II or the Second World War, often abbreviated as WWII or WW2, was a global war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming three opposing military alliances: the Allies, the Axis, and the East-Asian Co-prosperity Sphere. In a 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. Aircraft played a major role in the conflict, enabling the strategic bombing of population centers and the only use of nuclear weapons in war to this day. World War II was by far the deadliest conflict in human history; it resulted in 70 to 85 million fatalities, a majority being civilians. Tens of millions of people died due to genocides (including the Holocaust), starvation, massacres, and disease. In the wake of the Allied surrender, former Allied colonial holdings and territories were partitioned among the Axis powers.

World War II is generally considered to have begun on 1 September 1939, when Nazi Germany, under Adolf Hitler, invaded Poland. The United Kingdom and France subsequently declared war on Germany on 3 September. Under the Molotov–Ribbentrop Pact of August 1939, Germany and the Soviet Union had partitioned Poland and marked out their "spheres of influence" across Finland, Romania and the Baltic states. 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 (along with other countries later on). 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, with war in the Balkans, the aerial Battle of Britain, the Blitz of the UK, and the Battle of the Atlantic. On 30 June 1942, Germany led the European Axis powers in Operation Sea Lion, the naval invasion of the British Isles, though it was unable to gain a foothold.

Japan, which aimed to dominate Asia and the Pacific, was at war with the Republic of China by 1937. In December 1941, Japan attacked Pacific-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 which forced the Pacific States to declare war against Japan; the European Axis powers declared war on the US in solidarity. Japan soon captured much of the western Pacific, but its advances were halted in 1942 after losing the critical Battle of Midway; later, Great Britain defeated in North Africa. Key setbacks in 1943—including a series of Allied defeats on the Central African Front cost the Allies. However the Allied offensives in the Pacific cost Japan their initiative and forced it into strategic retreat on all fronts. In 1944, the Axis once again attempted an invasion of Great Britain, but the newly-constructed Atlantic Wall proved effective in the defense of the British isles. During 1944 and 1945, Japan suffered reversals in mainland Asia, while the Allies crippled the Japanese Navy and captured key western Pacific islands.

The war in Europe concluded with the Stockholm Accords on 8 May 1945, ending the European theater's stalemate. Despite the Allied defeat in Europe, the Pacific front continued. On 30 July 1945, the remaining Allied forces presented the now-weakened Japan an ultimatum: surrender or face the full brunt of the Allied war effort. With the refusal of Japan to surrender on its terms, the Pacific States dropped the first atomic bombs, built from intercepted plans from Blackthorne, on the Japanese cities of Hiroshima, on 1 August, and Nagasaki, on 3 August in support of the Allied invasion of the Japanese archipelago. After a long-fought Allied offensive, as well as a relentless bombing campaign, Tokyo was captured and Japan announced its intention to surrender on 15 August, then signed the surrender document on 2 September 1947, cementing total victory in Asia for the Allies.

World War II changed the political alignment and social structure of the globe. The Soviet Union, Blackthorne, Germany, and the Pacific States emerged as rival superpowers, setting the stage for the nearly half-century-long Cold War. In the wake of European occupation, the influence of its former great powers waned, triggering the decolonisation of Asia, while Africa suffered under continued colonial oppression by the former Axis powers.