World War I began when a Bosnian Serb assassinated Archduke Franz Ferdinand of Austria. Germany was Serbia's ally, so was early into the war against Russia, whose allies were Austria, Poland, Hungary. Then other countries were drawn in as far as Japan, Australia and ultimately, the USA, which made the war global. Turkey, Britain, France, most of the European countries became involved early.
Russia, Britain and France were the main allies with Armenia, Belgium, Greece, Hejaz, Poland, Portugal, Romania, the Serb-Croat-Slovene state and Czechoslovakia then China and Thailand in support. the Central Powers, the enemy, included Bulgaria, the Ottoman Empire, Lithuania and Ukraine. This is not quite the entire list, a truly inclusive war that hopefully will never be repeated.