Which former communist country disintegrated into several rival ethnically based states and saw several brutal civil wars during the 1990s?

Answer

Yugoslavia.

Q: What are the former communist countries? A: The former communist countries are the USSR (now Russia and other independent states), Yugoslavia, Poland, East Germany, Czechoslovakia, Romania, Bulgaria, Albania, and Hungary.
Q: Which of the former communist countries disintegrated into several rival ethnically based states and saw several brutal civil wars during the 1990s? A: Yugoslavia.