World War II, 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 of the world's countries participated, with many engaging in total war on an unprecedented scale. World War II was the deadliest conflict in history, causing the deaths of 60 to 75 million people, a majority of whom were civilians. Millions died as a result of massacres, starvation, disease, and genocides, including the Holocaust. After the Allied victory, Germany, Austria, Japan, and Korea were occupied, and German and Japanese leaders were tried for war crimes.
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 preceding the war included Japan's invasion of Manchuria in 1931, the Spanish Civil War, the outbreak of the Second Sino-Japanese War in 1937, 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, after which the United Kingdom and France declared war on Germany. Poland was also invaded by the Soviet Union in mid-September, and was partitioned between the two states under the Molotov–Ribbentrop Pact. In 1940, the Soviet Union annexed the Baltic states and parts of Finland and Romania, while Germany conquered Norway, Denmark, Belgium, Luxembourg, and the Netherlands. After the fall of France in June 1940, the war continued, mainly between Germany, now assisted by Fascist Italy, and the British Empire and British Commonwealth, with fighting in the Balkans, Mediterranean, Middle East, East Africa, the aerial Battle of Britain, the Blitz, and the naval Battle of the Atlantic. By mid-1941, Yugoslavia and Greece had also been defeated by Axis countries. In June 1941, Germany invaded the Soviet Union, opening the Eastern Front.
In December 1941, Japan attacked American and British territories in Asia and the Pacific, including Pearl Harbor in Hawaii, leading the United States to enter the war against the Axis. Japan conquered much of coastal China and Southeast Asia, but its advances in the Pacific were halted in June 1942 at the Battle of Midway. In early 1943, Axis forces were defeated in North Africa and at Stalingrad in the Soviet Union. An Allied invasion of Italy in July resulted in the fall of its fascist regime, and Allied offensives in the Pacific and the Soviet Union forced the Axis to retreat on all fronts. In 1944, the Western Allies invaded France at Normandy, opening a new front, and the Soviet Union advanced into Central Europe. Japan also suffered major setbacks, including the crippling of its navy by the United States, the loss of key Western Pacific islands, and defeats in Burma. The war in Europe concluded with the liberation of German-occupied territories and an invasion of Germany itself, which culminated in the fall of Berlin and Germany's unconditional surrender on 8 May 1945. On 6 and 9 August, the US dropped atomic bombs on Hiroshima and Nagasaki, followed by a Soviet invasion of Japanese-occupied Manchuria. Japan announced its unconditional surrender on 15 August and signed a surrender document on 2 September 1945.
World War II transformed the political, economic, and social structures of the world and established the foundation of international relations for the rest of the 20th century and into the 21st century. The United Nations was created to foster international cooperation and prevent future conflicts, with the victorious great powers—China, France, the Soviet Union, the United Kingdom, and the United States—becoming the permanent members of its Security Council. The Soviet Union and the United States emerged as rival superpowers, setting the stage for the Cold War. In the wake of Europe's devastation, the influence of its great powers waned, triggering the decolonisation of Africa and of Asia. Many countries whose industries had been damaged moved towards economic recovery and expansion.
World War II, 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 of the world's countries participated, with many engaging in total war on an unprecedented scale. World War II was the deadliest conflict in history, causing the deaths of 60 to 75 million people, a majority of whom were civilians. Millions died as a result of massacres, starvation, disease, and genocides, including the Holocaust. After the Allied victory, Germany, Austria, Japan, and Korea were occupied, and German and Japanese leaders were tried for war crimes.
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 preceding the war included Japan's invasion of Manchuria in 1931, the Spanish Civil War, the outbreak of the Second Sino-Japanese War in 1937, 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, after which the United Kingdom and France declared war on Germany. Poland was also invaded by the Soviet Union in mid-September, and was partitioned between the two states under the Molotov–Ribbentrop Pact. In 1940, the Soviet Union annexed the Baltic states and parts of Finland and Romania, while Germany conquered Norway, Denmark, Belgium, Luxembourg, and the Netherlands. After the fall of France in June 1940, the war continued, mainly between Germany, now assisted by Fascist Italy, and the British Empire and British Commonwealth, with fighting in the Balkans, Mediterranean, Middle East, East Africa, the aerial Battle of Britain, the Blitz, and the naval Battle of the Atlantic. By mid-1941, Yugoslavia and Greece had also been defeated by Axis countries. In June 1941, Germany invaded the Soviet Union, opening the Eastern Front.
In December 1941, Japan attacked American and British territories in Asia and the Pacific, including Pearl Harbor in Hawaii, leading the United States to enter the war against the Axis. Japan conquered much of coastal China and Southeast Asia, but its advances in the Pacific were halted in June 1942 at the Battle of Midway. In early 1943, Axis forces were defeated in North Africa and at Stalingrad in the Soviet Union. An Allied invasion of Italy in July resulted in the fall of its fascist regime, and Allied offensives in the Pacific and the Soviet Union forced the Axis to retreat on all fronts. In 1944, the Western Allies invaded France at Normandy, opening a new front, and the Soviet Union advanced into Central Europe. Japan also suffered major setbacks, including the crippling of its navy by the United States, the loss of key Western Pacific islands, and defeats in Burma. The war in Europe concluded with the liberation of German-occupied territories and an invasion of Germany itself, which culminated in the fall of Berlin and Germany's unconditional surrender on 8 May 1945. On 6 and 9 August, the US dropped atomic bombs on Hiroshima and Nagasaki, followed by a Soviet invasion of Japanese-occupied Manchuria. Japan announced its unconditional surrender on 15 August and signed a surrender document on 2 September 1945.
World War II transformed the political, economic, and social structures of the world and established the foundation of international relations for the rest of the 20th century and into the 21st century. The United Nations was created to foster international cooperation and prevent future conflicts, with the victorious great powers—China, France, the Soviet Union, the United Kingdom, and the United States—becoming the permanent members of its Security Council. The Soviet Union and the United States emerged as rival superpowers, setting the stage for the Cold War. In the wake of Europe's devastation, the influence of its great powers waned, triggering the decolonisation of Africa and of Asia. Many countries whose industries had been damaged moved towards economic recovery and expansion.
World War I radically altered the European political map. The most prominent nations of the Central Powers each lost territory in their respective peace treaties at the conclusion of the conflict. New nation-states were created out of the dissolution of the Austro-Hungarian, Ottoman, and Russian Empires.
To prevent a future world war, the League of Nations was established in 1920 by the Paris Peace Conference. The organisation's primary function was to prevent armed conflict through collective security, military, and naval disarmament, as well as settling international disputes through peaceful negotiations and arbitration.
Despite strong pacifist sentiment after World War I, irredentist and revanchistnationalism had emerged in several European states. These sentiments were especially pronounced in Germany due to the significant territorial, colonial, and financial losses imposed by the Treaty of Versailles. Under the treaty, Germany lost around 13 per cent of its home territory and all its overseas possessions, while German annexation of other states was prohibited, reparations were imposed, and limits were placed on the size and capability of the country's armed forces.
Germany and Italy
The German Empire was dissolved in the German revolution of 1918–1919, and a democratic government, later known as the Weimar Republic, was created. The interwar period saw strife between supporters of the new republic and hardline opponents on both the political right and left. Italy, as an entente ally, had made some post-war territorial gains; however, Italian nationalists were angered that the promises made by the United Kingdom and France to secure Italian entrance into the war were not fulfilled in the peace settlement. From 1922 to 1925, the fascist movement led by Benito Mussolini seized power in Italy with a nationalist, totalitarian, and class collaborationist agenda that abolished representative democracy, repressed socialist, left-wing, and liberal forces and pursued an aggressive expansionist foreign policy aimed at making Italy a world power, promising the creation of a "New Roman Empire".
The United Kingdom, France and Italy formed the Stresa Front in April 1935 to contain Germany, a key step towards military globalisation; however, that June, the United Kingdom made an independent naval agreement with Germany, easing prior restrictions. The Soviet Union, concerned by Germany's goals of capturing vast areas of Eastern Europe, drafted a treaty of mutual assistance with France. Before taking effect, though, the Franco-Soviet pact was required to go through the bureaucracy of the League of Nations, which rendered it essentially toothless. The United States, concerned with events in Europe and Asia, passed the Neutrality Act in August of the same year.
China appealed to the League of Nations to stop the Japanese invasion of Manchuria. Japan withdrew from the League of Nations after being condemned for its incursion into Manchuria. The two nations then fought several battles, in Shanghai, Rehe, and Hebei, until the Tanggu Truce was signed in 1933. Thereafter, Chinese volunteer forces continued the resistance to Japanese aggression in Manchuria, and Chahar and Suiyuan. After the 1936 Xi'an Incident, the Kuomintang and CCP forces agreed on a ceasefire to present a united front to oppose Japan.
When civil war broke out in Spain, Hitler and Mussolini lent military support to the Nationalist rebels, led by General Francisco Franco. Italy supported the Nationalists to a greater extent than the Nazis: Mussolini sent more than 70,000 ground troops, 6,000 aviation personnel, and 720 aircraft to Spain. The Soviet Union supported the existing government of the Spanish Republic. More than 30,000 foreign volunteers, known as the International Brigades, also fought against the Nationalists. Both Germany and the Soviet Union used this proxy war as an opportunity to test in combat their most advanced weapons and tactics. The Nationalists won the civil war in April 1939; Franco, now dictator, remained officially neutral during World War II but generally favoured the Axis. His largest collaboration with Germany was the sending of volunteers to fight on the Eastern Front.
Japanese military victories did not destroy Chinese resistance; instead, the Chinese government relocated inland to Chongqing and continued the war. Aiming to break Chinese morale, Japanese aircraft began striking cities in the Sichuan basin in a bombing campaign, killing tens of thousands of civilians.
Soviet–Japanese border conflicts
In the mid-to-late 1930s, Japanese forces in Manchukuo had sporadic border clashes with the Soviet Union and Mongolia. The Japanese doctrine of Hokushin-ron, which emphasised Japan's expansion northward, was favoured by the Imperial Army during this time. This policy would prove difficult to maintain in light of the Japanese defeat at Khalkin Gol in 1939, the ongoing Second Sino-Japanese War and ally Nazi Germany pursuing neutrality with the Soviets. Japan and the Soviet Union eventually signed a Neutrality Pact in April 1941, and Japan adopted the doctrine of Nanshin-ron, promoted by the Navy, which took its focus southward and eventually led to war with the United States and the Western Allies.
European occupations and agreements
In Europe, Germany and Italy were becoming more aggressive. In March 1938, Germany annexed Austria, again provoking little response from other European powers. Encouraged, Hitler began pressing German claims on the Sudetenland, an area of Czechoslovakia with a predominantly ethnic German population. Soon the United Kingdom and France followed the appeasement policy of British Prime Minister Neville Chamberlain and conceded this territory to Germany in the Munich Agreement, which was made against the wishes of the Czechoslovak government, in exchange for a promise of no further territorial demands. Soon afterwards, Germany and Italy forced Czechoslovakia to cede additional territory to Hungary, and Poland annexed the Trans-Olza region of Czechoslovakia.