World War II

World War II, or the Second World War (often abbreviated WWII or WW2), was a global military conflict which involved a majority of the world's nations, including all great powers, organized into two opposing military alliances: the Allies and the Axis. The war involved the mobilization of over 100 million military personnel, making it the most widespread war in history. In a state of "total war", the major participants placed their entire economic, industrial, and scientific capabilities at the service of the war effort, erasing the distinction between civilian and military resources. Over seventy million people, the majority of whom were civilians, were killed, making it the deadliest conflict in human history.

The start of the war is generally held to be September 1, 1939, with the German invasion of Poland and subsequent declarations of war on Germany by most of the countries in the British Empire and Commonwealth, and by France. Subsequently, the Soviet Union invaded Poland from the east side. Many countries were already at war before this date, such as Ethiopia and Italy in the Second Italo-Abyssinian War and Nationalist China and Japan in the Second Sino-Japanese War, and many who were not initially involved joined the war later, as a result of events such as the German invasion of the Soviet Union (Operation Barbarossa), and the attacks on Pearl Harbor and British colonies and subsequent declarations of war on Japan by Dutch and British Commonwealth.

In 1945 the war ended in a victory for the Allies. The Soviet Union and the United States subsequently emerged as the world's superpowers, setting the stage for the Cold War, which lasted for the next 46 years. The United Nations was formed in the hope of preventing another such conflict. The acceptance of the principle of self-determination accelerated decolonization movements in Asia and Africa, while Western Europe itself began moving toward integration.

World War I

World War I (abbreviated as WW-I, WWI, or WW1), also known as the First World War, the Great War, and the War to End All Wars, was a global miltary conflict which involved most of the world's great powers, assembled in two opposing alliances: the Allies of World War I centred around the Triple Entente and the Central Powers, centred around the Triple Alliance More than 70 million military personnel were mobilized in one of the largest wars in history. More than 15 million people were killed, making it one of the deadliest conflicts in history. During the conflict, the industrial and scientific capabilities of the main combatants were entirely devoted to the war effort.

The assassination, on 28 June 1914, of Archduke Franz Ferdinand of Austria, the heir to the throne of Austria-Hungary, is seen as the immediate trigger of the war, though long-term causes, such as imperialistic foreign policy, played a major role. The archduke's assassination at the hands of Serbian nationalist Gavrilo Princip resulted in demands against the Kingdom of Serbia. Several alliances that had been formed over the past decades were invoked, so within weeks the major powers were at war; with all having colonies, the conflict soon spread around the world.

By the war's end in 1918, four major imperial powers—the German, Russian, Austro-Hungarian and Ottoman Empires—had been militarily and politically defeated, with the last two ceasing to exist as autonomous entities. The revolutionized Soviet Union emerged from the Russian Empire, while the map of central Europe was completely redrawn into numerous smaller states. The League of Nations was formed in the hope of preventing another such conflict. The European nationalism spawned by the war, the repercussions of Germany's defeat, and the Treaty of Versailles would eventually lead to the beginning of World War II in 1939.

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