From Wikipedia
The fighting in World War I ended when the Armistice took effect at 11:00 am GMT on November 11, 1918. In the aftermath of the war the political, cultural, and social order of the world was drastically changed in many places, even outside the areas directly involved in the war. New countries were formed, old ones were abolished, international organizations were established, and many new and old ideas took a firm hold in people's minds.