World War II (September 1, 1939 – September 2, 1945) was a global conflict between two coalitions: the Allies and the Axis Powers. Nearly every nation in the world participated, and many mobilized their resources for total war. Tanks and aircraft played a major role, the latter enabling the strategic bombing of cities and the delivery of the only nuclear weapons used in warfare. World War II is the deadliest conflict in history, killing over 60 million people. Millions more died in massacres, including the Holocaust, and from genocide, starvation, and disease. Following 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 following 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 in 1931, the Spanish Civil War, the outbreak of the Second Sino-Japanese War in 1937, and Germany's occupation of Austria and the Sudetenland. World War II is generally considered to have begun on September 1, 1939, when Nazi Germany, led by Adolf Hitler, invaded Poland, prompting the United Kingdom and France to declare war on Germany. In mid-September, the Soviet Union also invaded Poland, and it was partitioned between Germany and the Soviet Union under the Molotov–Ribbentrop Pact. In 1940, the Soviet Union occupied the Baltic countries and parts of Finland and Romania, while Germany occupied Norway, Belgium, Luxembourg, and the Netherlands. After the fall of France in June 1940, the war continued primarily between Germany, now aided by Fascist Italy, and the British Empire/British Commonwealth, with fighting in the Balkans, the Mediterranean and Middle East, East Africa, the aerial Battle of Britain and the Blitz, and the naval Battle of the Atlantic. By mid-1941, Yugoslavia and Greece had also fallen to the Axis. In June 1941, Germany invaded the Soviet Union, opening the Eastern Front and initially occupying large areas alongside Axis allies.
In December 1941, Japan attacked American and British territories in Asia and the Pacific, including Pearl Harbor in Hawaii, leading the United States to join the war against the Axis. Japan conquered coastal China and much of Southeast Asia, but its advance in the Pacific was halted at the Battle of Midway in June 1942. In early 1943, Axis forces were defeated in North Africa and at Stalingrad in the Soviet Union. In July, the Allied invasion of Italy ended its fascist regime, and Allied attacks in the Pacific and the Soviet Union forced Axis forces to retreat on all fronts. In 1944, the Western Allies invaded France at Normandy, and the Soviet Union advanced in Central Europe. Meanwhile, Japan suffered major setbacks, including the weakening of its navy by the United States, the loss of key islands in the Western Pacific, and defeats in South-Central China and Burma.
The war in Europe ended with the liberation of German-occupied territories and the Allied invasion of Germany, resulting in the capture of Berlin by Soviet troops and Germany's unconditional surrender on May 8, 1945. On August 6 and 9, the US dropped atomic bombs on Hiroshima and Nagasaki, Japan. Faced with the threat of Allied attack and the possibility of atomic bombing, and the Soviet Union's declaration of war and invasion of Manchuria, Japan announced its unconditional surrender on 15 August, and signed the surrender document on 2 September 1945.
World War II transformed the world's political, economic, and social structure, laying the foundation for international relations for the rest of the 20th century and into the 21st. The United Nations was created to promote international cooperation and prevent future conflicts, with the victorious major powers—China, France, the Soviet Union, the UK, and the US—becoming permanent members of its Security Council. The Soviet Union and the US emerged as rival superpowers, leading to the Cold War that lasted half a century. Following the devastation of Europe, the influence of its major powers diminished, leading to the decolonization of Africa and Asia. Many countries whose industries had suffered losses embarked on economic recovery and expansion.
Start and end dates
Most historians agree that World War II began with the German invasion of Poland on September 1, 1939, and the United Kingdom and France's declaration of war on Germany two days later. Other proposed start dates for the Pacific War include the outbreak of the Second Sino-Japanese War on July 7, 1937, or the first Japanese invasion of Manchuria on September 18, 1931. Other proposed start dates for World War II include the Italian invasion of Abyssinia on October 3, 1935. British historian Antony Beevor places the beginning of World War II at the Battles of Khalkhin Gol, fought between Japan and the forces of Mongolia and the Soviet Union from May to September 1939. Others consider the Spanish Civil War to be the beginning or the beginning of World War II.
There is also disagreement on the exact date the war ended. At the time, it was generally believed that the war ended with the armistice of August 15, 1945 (V-J Day), rather than with Japan's formal surrender on September 2, 1945, which officially ended the war in Asia. A peace treaty was signed between Japan and the Allies in 1951. A 1990 treaty on the future of Germany allowed East and West Germany to be reunited. No formal peace treaty was ever signed between Japan and the Soviet Union, although the state of war between the two countries was ended by the 1956 Soviet–Japanese Joint Declaration, which also restored full diplomatic relations between them.
Background of the war
After World War I
World War I completely altered the political map of Europe with the defeat of the Central Powers – Austria-Hungary, Germany, Bulgaria, and the Ottoman Empire – and the Bolshevik seizure of power in Russia in 1917, creating the Soviet Union. Meanwhile, victorious World War I allies, such as France, Belgium, Italy, Romania, and Greece, gained territory, and the collapse of the Austro-Hungarian, Ottoman, and Russian empires led to the formation of new nation-states.
To prevent a future world war, the Paris Peace Conference of 1920 established the League of Nations. The organization's primary goals were to prevent armed conflict through collective security, military and naval disarmament, and the resolution of international disputes through peaceful negotiations and arbitration.
Despite strong pacifist sentiment after World War I, irredentist and revanchist nationalism emerged in many European countries. These sentiments were particularly strong in Germany, as the Treaty of Versailles had resulted in significant territorial, colonial, and financial losses. Under the treaty, Germany lost approximately 13 percent of its territory and all of its foreign lands, while German occupation of other countries was prohibited, reparations were imposed, and limits were placed on the size and capabilities of the country's military.
Germany and Italy
The German Revolution of 1918–1919 ended the German Empire, and a democratic government was established, later known as the Weimar Republic. The interwar period was marked by conflict between supporters of the new republic and staunch opponents on both the political right and left. Italy, as an Entente ally, had gained some territorial gains after the war; however, Italian nationalists were angry that the promises made by the United Kingdom and France to Italy upon Italy's entry 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 collaborative agenda that abolished representative democracy, suppressed socialist, left-wing, and liberal forces, and pursued an aggressive expansionist foreign policy aimed at making Italy a world power, promising to create a "New Roman Empire".
After a failed attempt to overthrow the German government in 1923, Adolf Hitler finally became Chancellor of Germany in 1933 when President Paul von Hindenburg and the Reichstag appointed him. After Hindenburg's death in 1934, Hitler declared himself Führer of Germany and abolished democracy, supporting a radical, racially motivated change in the world order, and soon launched a massive rearmament campaign. France, in an attempt to cement its alliance with Italy, gave Italy free rein in Ethiopia, which Italy wanted as a colonial possession. The situation worsened in early 1935 when the Saar Basin region was legally reintegrated into Germany, and Hitler rejected the Treaty of Versailles, accelerated his rearmament program, and began conscription.












