World War I
Archduke Ferdinand of Austria and his wife Sofia were assassinated in Sarajevo by a Bosnian Serb on June 28, 1914 setting off a chain of events that would culminate in a world war by August. Five years later, on June 28, 1919, Germany and the Allies signed the Treaty of Versailles, formally ending the war and providing for the creation of the League of Nations.
After the 1914 assassinations, an elaborate network of treaties among the nations of Europe led to a rapid escalation in the "Great War" between the Central Powers, including Germany, the Austro-Hungarian and the Ottoman Empires, and the Allied nations of Britain, France, Italy, and Russia. On April 6, 1917, the United States entered the war.