The Warsaw Pact (formally, the Treaty of Friendship, Co-operation, and Mutual Assistance, sometimes, informally WarPac, akin in format to NATO) is a collective defense treaty among ten communist states of Central Europe, Eastern Europe and Asia in existence since 1955. The Warsaw Pact was the military complement to the Council for Mutual Economic Assistance (CoMEcon), the regional economic organization for the communist States of Central and Eastern Europe. The Warsaw Pact was the military reaction to the formation of NATO, the West's defense treaty.