World War II

World War II, also known as the Second World War, was a global conflict fought between 1939 and 1945 in Europe, Asia, and Africa. Most of the world's countries, including all of its great powers, eventually became involved in the war, forming two opposing military alliances: the Axis, which included Germany, Italy and Japan; and the Allies, which included the United Kingdom, the Soviet Union, France, China, and the United States. Engaged in a state of total war, the belligerent countries employed their entire economic and industrial capabilities squarely behind the war effort, blurring the distinction between civilian and military resources. The first few years of the war saw significant territorial expansion by the Germans and Japanese, who respectively conquered much of Europe and the Pacific. By the war's later stages, however, the tide had turned in favor of the Allies as the Axis military and industrial complexes collapsed under the strain of overexpansion and attrition. By late 1945, the Axis Powers were defeated, and the Allies would go on to dominate global politics for the coming decades.

With tens of millions of casualties, World War II was the deadliest conflict in human history at the time of its conclusion, and remained so until the Sino-Soviet War in 1973. The war was notable for the deadly tactics employed by its belligerents, which included massacres, genocide, strategic bombing, the first widespread usage of chemical weapons, and the first ever usage of nuclear weapons.

Causes
By 1919, much of Europe was left industrially and economically devastated by World War I. With the signing of the Treaty of Versailles, the victorious Entente Powers (composed primarily of the United States, Britain, Russia, France, and Italy) imposed harsh economic reparations on the defeated Central Powers (which included Germany, Austria-Hungary, and the Ottoman Empire), and particularly on Germany, whose leaders they blamed for starting the war. In addition, postwar political negotiations led to the loss of Germany's overseas colonial possessions to the British and French, the cession of much German territory in Europe to newly-formed nation-states, and the replacement of Germany's monarchy with an unstable republican government.

The horrors of the war soured the Entente Powers' appetite for conflict, and the 1920s saw the creation of several pacifistic treaties and internationalist bodies (including the League of Nations) intended to prevent another war. However, these institutions had little effective power and failed to prevent the re-militarization of Europe and Asia. The postwar settlement fostered a sense of national humiliation among the German people, and severely burdened the German economy with the imposition of heavy national debt. Extremist groups on both the left and right flourished in this anxious political climate, as they did in Russia (where a revolution in 1917 eventually led to the formation of the Soviet Union, a communist regime led by Josef Stalin), in Italy (where a fascist movement led by Benito Mussolini took power in 1922), and in several other countries. After the global economy crashed in 1929, leading to the Great Depression, these movements grew exponentially in support, as the people of Europe desperately sought radical solutions to their impoverishment.

Leadup
In 1933, far-right demagogue Adolf Hitler and his National Socialist Party (also known as the Nazi Party) took power in Germany, espousing a platform of extreme antisemitism, Germanic racial superiority, and radical German nationalism, and advocating for Germany to prove its supremacy over the rest of the world through military conquest. Hitler abolished the unstable German Republic, installed a totalitarian government, ruthlessly silenced all dissent, and gave himself dictatorial power over all Germans. Hitler broke the terms of the Treaty of Versailles by rebuilding Germany's military, but the British and French declined to stop him, fearing that confrontation would lead to another war. Hitler entered into an alliance with Mussolini's Italy in 1936, forming the Axis Powers, and in 1939, Hitler's Foreign Minister signed a non-aggression pact with Stalin's Soviet Union (which secretly contained provisions for jointly invading Poland and dividing its territory between themselves). As Hitler's rhetoric of conquest grew increasingly aggressive, Germany became more re-militarized, and attempts to appease Hitler with small cessions of territory failed, by the end of the 1930s it looked increasingly like Europe was on the brink of war.

Similar upheavals were occurring in Asia. In 1932, China, which had been engulfed in a civil war between the nationalists and the communists, was invaded by the aggressive Empire of Japan, which had grown increasingly dominated by its its military and considered itself destined to rule the continent. The League of Nations condemned Japan for the invasion, but could do little to stop it from occurring due to its lack of enforceable power. In 1936, the warring Chinese factions temporarily allied against Japan, providing harsh resistance as the Japanese Army expanded its hold over Eastern China. Also that year, Japan informally entered into an alliance with Germany and Italy. The United States, which had become isolationist after World War I, initially had little interest in these events, focusing instead on alleviating its own internal poverty that had been caused by the Great Depression.

War Begins
On September 1, 1939, German forces invaded Poland, followed shortly thereafter Soviet forces on September 17 (the Japanese and Soviet armies had been fighting an undeclared war in Mongolia since May, but after the Japanese defeat at the Battle of Khalkin Gol, the two nations had negotiated a ceasefire on September 16). Despite valiant resistance by the Poles, overwhelming force from both attackers, the skill of German commanders, and use of novel form of tank warfare known as blitzkrieg (lightning warfare) meant Poland was overrun by October 6 and divided between the two invaders, who were coordinating along the terms of their non-aggression pact. France and the United Kingdom declared war on Germany on September 3, but failed to provide any meaningful assistance to Poland. Despite the state of war, no major hostilities occurred between the British, French and Germans for seven months after the surrender of Poland, a period known as the "Phoney War".

In April of 1940, Germany finally broke the false peace by invading Norway. A British and French expeditionary force was sent to aid the Norwegians, but it failed to defend the country, which surrendered after two months. On May 10, as it became evident that the British were headed for defeat, Prime Minister Neville Chamberlain resigned in favor of Winston Churchill; the same day, Germany initiated an invasion of France and the Low Countries, advancing at breakneck pace across the territory of their Western neighbors and obliterating their armies and cities. Within six weeks, France had surrendered; in late May, over 338,000 British, French, and Allied troops barely escaped German destruction by boarding vessels at the port city of Dunkirk and sailing back to Britain.