World War I /ˌwɜːld wɔː ˈwʌn $ ˌwɜːrld wɔːr-/ BrE AmE ( also the First World War )
(1914–1918) a war in Europe fought between France, the UK and its ↑ empire , Russia, and the US on one side (known together as ‘the Allies’), and Germany, Austria-Hungary, and Turkey on the other side. The war started as a result of the murder in Sarajevo of the Archduke Franz Ferdinand, a member of the Austrian royal family.