World War One (1914-1918)

Involved all of the world's great powers divided into two opposing alliances: The Allies and the Central Powers. By the end of the war, the German, Russian, Austro-Hungarian, and Ottoman Empires had been defeated. The war ended with signing of the Treaty of Versailles.

World War Two (1939-1945)

Involved two opposing alliances: The Allies and the Axis. The end of the war resulted in the defeat of Germany, Japan and Italy. 

The Cold War (1947-1991)

A period of intense hostility between the two global powers: the Soviet Union and the United States. Other countries were forced to pick a side. In the end, the Soviet Union dissolved, and the United States became the unipolar power.