World War II[b] or the Second World War (1 September 1939 – 2
September 1945) was a global conflict between two coalitions:
the Allies and the Axis powers. Nearly all the world's countries—including
all the great powers—participated, with many investing all available
economic, industrial, and scientific capabilities in pursuit of total war,
blurring the distinction between military and civilian
resources. Tanks and aircraft played major roles, with the latter enabling
the strategic bombing of population centres and delivery of the only two
nuclear weapons ever used in war. World War II was the deadliest
conflict in history, resulting in 70 to 85 million deaths, more than half
being civilians. Millions died in genocides, including the Holocaust of
European Jews, as well as from massacres, starvation, and disease.
Following the Allied powers' victory, Germany, Austria, Japan,
and Korea were occupied, and war crimes tribunals were
conducted against German and Japanese leaders.
The causes of World War II included unresolved tensions in the aftermath
of World War I and the rise of fascism in Europe and militarism in Japan.
Key events leading up to the war included Japan's invasion of Manchuria,
the Spanish Civil War, the outbreak of the Second Sino-Japanese War, and
Germany's annexations of Austria and the Sudetenland. World War II is
generally considered to have begun on 1 September 1939, when Nazi
Germany, under Adolf Hitler, invaded Poland, prompting the United
Kingdom and France to declare war on Germany. Poland was divided
between Germany and the Soviet Union under the Molotov–Ribbentrop
Pact, in which they had agreed on "spheres of influence" in Eastern
Europe. In 1940, the Soviets annexed the Baltic states and parts of
Finland and Romania. After the fall of France in June 1940, the war
continued mainly between Germany and the British Empire, with fighting
in the Balkans, Mediterranean, and Middle East, the aerial Battle of
Britain and the Blitz, and naval Battle of the Atlantic. Through a series of
campaigns and treaties, Germany took control of much of continental
Europe and formed the Axis alliance with Italy, Japan, and other countries.
In June 1941, Germany led the European Axis in an invasion of the Soviet
Union, opening the Eastern Front and initially making large territorial
gains.
Japan aimed to dominate East Asia and the Asia-Pacific, and by 1937 was
at war with the Republic of China. In December 1941, Japan attacked
American and British territories in Southeast Asia and the Central Pacific,
including Pearl Harbor in Hawaii, which resulted in the US and the UK
declaring war against Japan, and the European Axis declaring war on the
US. Japan conquered much of coastal China and Southeast Asia, but its
advances in the Pacific were halted in mid-1942 after its defeat in the
naval Battle of Midway; Germany and Italy were defeated in North
Africa and at Stalingrad in the Soviet Union. Key setbacks in 1943—
including German defeats on the Eastern Front, the Allied invasions of
Sicily and the Italian mainland, and Allied offensives in the Pacific—cost
the Axis powers their initiative and forced them into strategic retreat on
all fronts. In 1944, the Western Allies invaded German-occupied France at
Normandy, while the Soviet Union regained its territorial losses and
pushed Germany and its allies westward. At the same time, Japan suffered
reversals in mainland Asia, while the Allies crippled the Japanese
Navy and captured key islands.
The war in Europe concluded with the liberation of German-occupied
territories; the invasion of Germany by the Western Allies and the Soviet
Union, culminating in the fall of Berlin to Soviet troops; Hitler's suicide;
and the German unconditional surrender on 8 May 1945. Following the
refusal of Japan to surrender on the terms of the Potsdam Declaration, the
US dropped the first atomic bombs on Hiroshima and Nagasaki on 6 and 9
August. Faced with an imminent invasion of the Japanese archipelago, the
possibility of further atomic bombings, and the Soviet declaration of
war against Japan and its invasion of Manchuria, Japan announced its
unconditional surrender on 15 August and signed a surrender
document on 2 September 1945, marking the end of the war.
