World War 1 or First World War was known as the Great War or "The war to end all wars", before the beginning of the Second World War.
The principal countries involved in this war were Russia, France, Britain, Italy and the United States of America in one side, and Germany, Austria-Hungary, and Turkey on the other side, forming two opposed alliances: The Allies and the Central Powers.
This war began because of a Serbian nationalist, who killed Archduke Ferdinand, heir of the Austrian throne. Because of this act of terrorism, a great war started, and that come to be known as the major European conflict in a hundred thousand years.