The Treaty of Friendship, Cooperation, and Mutual Assistance (TFCMA), known better as the Warsaw Pact, was a defence treaty signed in May of 1955 as a response to western aggression. The Warsaw Pact today refers to the resulting military alliance among Eastern European nations.
Czechoslovak Socialist Republic
Union of Soviet Socialist Republics
People's Socialist Republic of Albania was a founding member but withdrew in 1968.
The Warsaw Pact originated from Czechoslovak leadership sought to create a defensive pact with East Germany and Poland due to concerns about a remilitarised West Germany after their NATO membership.