Bulgaria part of the Warsaw Pact - 1955

The Warsaw Pact or Warsaw Treaty Organization, officially named the Treaty of Friendship, Co-operation and Mutual Assistance was an organization of Central and Eastern European communist states. It was established in 1955 in Warsaw, Poland to counter the alleged threat from the NATO alliance. The creation of the Warsaw Pact was prompted by the integration of a "re-militarized" West Germany into NATO on May 9, 1955 via ratification of the Paris Peace Treaties.

The Pact lasted throughout the Cold War until certain member nations began withdrawing in 1991, following the collapse of the Eastern bloc and political changes in the Soviet Union. The treaty was signed in Warsaw, Poland on May 14, 1955 and official copies were made in Russian, Polish, Czech and German.

Members
* Soviet Union
* Poland Poland
* East Germany East Germany
* Czechoslovakia Czechoslovakia
* Bulgaria Bulgaria
* Hungary Hungary
* Romania
* Albania (withdrew its support in 1961 over ideological differences, formally left in 1968)

On 12 March 1999, the former Warsaw Pact members and successor states Hungary, Poland and the Czech Republic joined NATO. Bulgaria, Estonia, Latvia, Lithuania, Romania, and Slovakia followed suit in March 2004.

On 1 May 2004, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, and Slovakia became members of the European Union. This group was followed in 2007 by Romania and Bulgaria.