The Great War ravaged Europe from July 28, 1914 until November 11, 1918, killing 9 million combatants. Though sparked by the assassination of Archduke Franz Ferdinand of Austria, the threat of imperialism was the conflict's true underlying cause. It was a war that eventually garnered global involvement with Japan and the United States joining the Allies (the United Kingdom, France, and the Russian Empire) and the Ottoman Empire joining the Central Powers of Germany and Austria-Hungary. "The most costly and destructive war in the world's history," to quote historian H.P. Willmott, was also a conflict that later triggered revolutions in many of the nations that participated.
Here are ten powerful photos from the war that changed the world.