One month after a Bosnian-Serb assassinated Austrian Archduke Franz Ferdinand and his wife, Sophie, Duchess of Hohenberg, on a street corner in Sarajevo, Austria-Hungary declared war on Serbia, effectively beginning World War I.
Ferdinand's murder sent the Great Powers into a war that would last five years and cost the lives of 10 million troops.
Thought of as the "war to end all wars," World War I marked a number of firsts in military conflict, including the use of planes, tanks, and chemical weapons.
On June 28, 1919, the victorious Allied leaders signed the Treaty of Versailles, officially ending World War I and spurring German nationalism, which in turn gave Nazi leader Adolf Hitler a political platform.
Here's a few colorized photographs published by The Open University showing life during World War I.
SEE ALSO: Haunting visions of World War I live on in these overlay photos
Trench warfare was one of the hallmarks of World War I.
Soldiers could spend the majority of their deployments in the trenches. Here, a soldier receives a haircut from a barber on the Albanian front.
Here, a German Field Artillery crew poses with its gun at the start of the war in 1914.
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