World War I, also called Great War, an international conflict which involved most of the nations of Europe along with Russia, the United States, the Middle East and other nations, and it was one of the greatest watersheds of 20th-century geopolitical history. The war attracted Central Powers, mainly Germany, Austria-Hungary and Turkey against France, Great Britain, Russia, Italy, Japan and the United States. The war was unprecedented in the slaughter, carnage and destruction it caused. The war ended with the defeat of the Central Powers and it led to the fall of four great imperial dynasties - Germany Russia, Austria-Hungary and Turkey. It resulted the Bolshevik Revolution in Russia, and, destabilizing European society, laid the basis for World War II.