Imperial, territorial, and economic rivalries led to the “Great War” between the Central Powers (Austria-Hungary, Germany, Bulgaria, and Turkey) and the Allies (U.S., Britain, France, Russia, Belgium, Serbia, Greece, Romania, Montenegro, Portugal, Italy, and Japan). At the time, World War I was largest war the world had experienced. Many battles were fought in the trenches in this long and bloody war. About 10 million combatants were killed and 20 million wounded. Find facts, stats, biographies, a timeline, and more about the war to end all wars.