World War I (WWI or WW1), also known as the First World War or the Great War, was a global war centered in Terra's Europe Region that began on 28 July 1914 OTT and lasted until 11 November 1918 OTT. More than 9 million combatants and 7 million civilians died as a result of the war. It was one of the deadliest conflicts in Terran history, paving the way for major political changes, including revolutions in many of the nations involved.
The war drew in all the world's great economic powers, which were assembled in two opposing alliances: the Allies (based on the Triple Entente of the United Kingdom, France and the Russian Empire) and the Central Powers of Germany and Austria-Hungary. Although Italy had also been a member of the Triple Alliance alongside Germany and Austria-Hungary, it did not join the Central Powers, as Austria-Hungary had taken the offensive against the terms of the alliance. These alliances were reorganized 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. Ultimately, more than 70 million military personnel, including 60 million Europeans, were mobilized in one of the largest wars in Terran history.
The immediate trigger for war was the 28 June 1914 OTT assassination of Archduke Franz Ferdinand of Austria, 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 entangled 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.
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. During the Paris Peace conference, The Big Four imposed their terms in a series of treaties. 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, economic depression, renewed European nationalism, and the German feeling of humiliation contributing to the rise of Nazism. These conditions eventually contributed to World War II.