"A major international conflict fought from 1914 to 1918, World War I was the most deadly and destructive war the world had ever seen to that time. More than 25 countries eventually participated, aligned with either the Allied or the Central powers. The Allies—who won the war—included primarily France, Great Britain, Russia, Italy, Japan, and, from 1917, the United States. The Central Powers consisted mainly of Germany, Austria-Hungary, and the Ottoman Empire (Turkey). World War I felled four great imperial dynasties, in Germany, Russia, Austria-Hungary, and Turkey."