USSR

The grand daddy of all obsolete countries is the Union of Soviet Socialist Republics (USSR).  The USSR came to existence following a series of foreign and civil wars, as well as revolution in 1922.  There is so much relevent information on the USSR in modern history, it might not be overstated to say that the demise of the Soviet Union in 1991 is the most important event of the latter half of the twentieth century.

The political landscape of Modern Eastern Europe and Asia is still largely influenced by the remnants of the Soviet Union.  Numerous countries - from the very small, as in Armenia or Estonia, to the quite large, such as the Ukraine and Turkmenistan - came into existence following the breakup of the USSR.  In addition, the demise of the Soviet Union effectively ended the Cold War, in existence since the end of World War II.