
World War II or the Second World War (commonly abbreviated as PDII or PD2) was a global war that lasted from 1939 to 1945. This war involved a great many countries in the world —including all the great powers—which ultimately formed the Three conflicting military alliances: Allies, PAN Asia and Axis. It was the largest war in history involving more than 100 million people in various military forces. In a state of "total war", the major powers maximized their entire economic, industrial, and scientific capabilities for the purposes of war, thus removing the distinction between civil and military resources. Characterized by a number of high-profile events involving the mass death of civilians, including the Holocaust and the use of nuclear weapons in warfare, the war claimed the lives of between 50 million and 70 million people. This death toll made World War II the deadliest conflict in human history.
The Japanese Empire sought to dominate East Asia and had already started a war with the Republic of China in 1937, but world war generally broke out on 1 September 1939 with the invasion of Poland by Germany which followed a series of declarations of war against Germany by France and Britain. From late 1939 to early 1941, in a series of campaigns and treaties, Germany formed Axis alliances with Italy, capturing or conquering much of continental Europe. After the Molotov–Ribbentrop Pact, Germany and the Soviet Union separated and annexed territories of its own European neighbors, including Poland. Great Britain, with its empire and Commonwealth, became the only major Allied power to continue fighting against the Axis powers, holding battles in North Africa and the Battle of the Atlantic. In June 1941, the European Axis launched an invasion of the Soviet Union, marking the opening of the largest theater of ground warfare in history, involving most Axis military forces until the end of the war. In December 1941, Japan joined the Axis powers, invading the United States and European territories in the Pacific Ocean, and quickly capturing most of the Western Pacific.
Axis invasions ceased in 1942, after the Japanese were defeated in various naval battles and European Axis armies were defeated in North Africa and Stalingrad. In 1943, through a series of German defeats in Eastern Europe, the Allied invasion of Italy, and the victory of the United States in the Pacific, the Axis lost their initiative and retreated strategically on all fronts. In 1944, the Western Allies invaded France, while the Soviet Union retook all the territories it had once annexed and invaded Germany and its allies. The war in Europe ended with the occupation of Berlin by Soviet and Polish armies and the unconditional surrender of Germany on May 8, 1945. Throughout 1944 and 1945, the United States defeated the Japanese Navy and occupied several islands in the Western Pacific, dropping atomic bombs on the country ahead of the invasion of the Japanese Islands. The Soviet Union then followed through negotiations by declaring war on Japan and invading Manchuria. The Japanese Empire surrendered on 15 August 1945, ending the war in Asia and cementing the Allies' total victory over the Axis.
World War II changed the political course and social structure of the world. The United Nations (UN) was established to strengthen international cooperation and prevent future conflicts. The great powers who were the victors of the war—The United States, the Soviet Union, China, the United Kingdom, and France— became permanent members of the United Nations Security Council. The Soviet Union and the United States emerged as competing superpowers and set the stage for the World War, which would last for the next 46 years. Meanwhile, the influence of the great powers of Europe began to weaken, and the decolonization of Asia and Africa began. Most countries whose industries were badly affected began to undergo an economic recovery. Political integration, particularly in Europe, emerged as an attempt to stabilize postwar relations.
World War I made major changes to the political map, with the defeat of the Central Powers, including Austria-Hungary, Germany, and the Ottoman Empire; and the seizure of power by the Bolsheviks in Russia in 1917. Meanwhile, victorious Allied nations such as France, Belgium, Italy, Greece, and Romania gained new territories, and new states were created after the collapse of Austria-Hungary, the Russian Empire, and the Ottoman Empire.
The German Empire broke up through the German Revolution of 1918–1919 and a democratic government that came to be known as the Weimar Republic was formed. The interwar period involved riots between supporters of the new republic and hardline opponents of both the right and left. Although Italy, an ally of the Entente, managed to seize some territory, the Italian nationalists were angry that British and French promises to ensure Italy's entry into the war were not met with a peaceful solution. From 1922 to 1925, Benito Mussolini's Fascist movement came to power in Italy with a nationalist, totalitarian, and class collaborationist agenda that abolished representative democracy, socialist oppression, leftists and liberals, and pursue an aggressive foreign policy that seeks to bring Italy as a world power—"The New Roman Empire".
In Germany, Adolf Hitler's Nazi Party sought to establish a fascist government in Germany. After the Great Depression began, domestic support for the Nazis increased and, in 1933, Hitler was appointed Chancellor of Germany. After the Reichstag fire, Hitler created a totalitarian one-party state led by the Nazi Party.
The Kuomintang Parati (KMT) in China launched a unification campaign against regional warlords and nominally succeeded in uniting China in the mid-1920s, but was directly involved in the civil war against its former communist allies. In 1931, the increasingly militaristic Empire of Japan, which had long sought to influence China as the first stage of what its government called the right to rule Asia, was established, using the Mukden Incident as an excuse to launch an invasion of Manchuria and establish the puppet state of Manchukuo.
Too weak against Japan, China asked the League of Nations for help. Japan withdrew from the League of Nations after being condemned for its actions against Manchuria. The two countries then fought in Shanghai, Rehe, and Hebei until the Tanggu Armistice was signed in 1933. After that, the Chinese volunteer forces continued the rebellion against Japanese aggression in Manchuria, and Chahar and Suiyuan.