World War I (WWI), also known as the First World War or the Great War, was a global war centered in Europe that began on 28 July 1914 and lasted until 11 November 1918.
Although a resurgence of imperialism was an underlying cause, the immediate trigger for war was the 28 June 1914 assassination of Archduke Franz Ferdinand of Austria, heir to the throne of Austria-Hungary, by Yugoslav nationalist Gavrilo Princip in Sarajevo. This set off a diplomatic crisis when Austria-Hungary delivered an ultimatum to the Kingdom of Serbia, and international alliances formed over the previous decades were invoked. Within weeks, the major powers were at war and the conflict soon spread around the world.
The war drew in all the world’s economic great powers, which were assembled in two opposing alliances: the Allies (based onthe Triple Entente of the United Kingdom, France and the Russian Empire) and the Central Powers of Germany and Austria-Hungary. These alliances were both re-organised and expanded as more nations entered the war: Italy, Japan and the United States joined the Allies, and the Ottoman Empire and Bulgaria the Central Powers.
More than 9 million combatants were killed; a casualty rate exacerbated by the belligerents’ technological and industrial sophistication, and tactical stalemate. It was one of the deadliest conflicts in history, paving the way for major political changes, including revolutions in many of the nations involved.
Ultimately, more than 70 million military personnel, including 60 million Europeans, were mobilized in one of the largest wars in history.
By the end of the war, four major imperial powers—the German, Russian, Austro-Hungarian and Ottoman empires—ceased to exist. The successor states of the former two lost substantial territory, while the latter two were dismantled. The maps of Europe and Southwest Asia were redrawn, with several independent nations restored or created.
The League of Nations was formed with the aim of preventing any repetition of such an appalling conflict. This aim, however, failed with weakened states, renewed European nationalism and the German feeling of humiliation contributing to the rise of fascism. All of these conditions eventually led to World War II.