On July 28, 1914, a month after a Bosnian-Serb assassinated Austrian Archduke Franz Ferdinand on a street corner in Sarajevo, the Austro-Hungarian Empire declared war on Serbia, beginning World War I.
Three bloody years later, the US would enter the conflict on the side of the Allies, declaring war on the Central Powers on April 6, 1917.
World War I saw a number of military innovations, including the use of planes, tanks, and chemical weapons. An armistice on November 11, 1918, was followed by the Treaty of Versailles, officially ending World War I, on June 28, 1919.
Here are a few colorized photographs published by The Open University showing life during World War I.