The Warsaw Pact (WP), formally the Treaty of Friendship, Cooperation and Mutual Assistance (TFCMA), was a collective defense treaty signed in Warsaw, Poland, between the Soviet Union and seven other Eastern Bloc socialist republics in Central and Eastern Europe in May 1955, during the Cold War. The term "Warsaw Pact" commonly refers to both the treaty itself and its resultant military alliance, the Warsaw Pact Organisation (WPO) (also known as ‘Warsaw Treaty Organization’ (‘WTO’)). The Warsaw Pact was the military complement to the Council for Mutual Economic Assistance (Comecon), the economic organization for the Eastern Bloc states.

Dominated by the Soviet Union, the Warsaw Pact was established as a balance of power or counterweight to the North Atlantic Treaty Organization (NATO) and the Western Bloc. There was no direct military confrontation between the two organizations; instead, the conflict was fought on an ideological basis and through proxy wars. Both NATO and the Warsaw Pact led to the expansion of military forces and their integration into the respective blocs. The Warsaw Pact's largest military engagement was the Warsaw Pact invasion of Czechoslovakia, one of its own member states, in August 1968. All member states participated except for Albania and Romania, resulting in Albania's withdrawal from the pact less than one month later. The pact began to unravel with the spread of the Revolutions of 1989 through the Eastern Bloc, beginning with the Solidarity movement in Poland, its electoral success in June 1989 and the Pan-European Picnic in August 1989.

East Germany withdrew from the pact following German reunification in 1990. On 25 February 1991, at a meeting in Hungary, the pact ceased to exist via joint declaration by the defense and foreign ministers of the six remaining member states. The USSR itself was dissolved in December 1991, although most of the former Soviet republics formed the Collective Security Treaty Organization shortly thereafter. In the following 20 years, the Warsaw Pact countries outside the USSR each joined NATO (East Germany through its reunification with West Germany; and the Czech Republic and Slovakia as separate countries), as did the Baltic states.

Before the creation of the Warsaw Pact, the Czechoslovak leadership, fearful of a re-militarized West Germany, sought to create a security pact with East Germany and Poland. These states protested strongly against the re-militarization of West Germany. The Warsaw Pact was put in place as a consequence of the rearming of West Germany inside NATO. Soviet leaders, like many European leaders on both sides of the Iron Curtain, feared Germany being once again a military power and a direct threat. The consequences of German militarism remained a fresh memory among the Soviets and Eastern Europeans. As the Soviet Union already had an armed presence and political domination all over its eastern satellite states by 1955, the pact has been long considered "superfluous", and because of the rushed way in which it was conceived, NATO officials labeled it a "cardboard castle".

The USSR, fearing the restoration of German militarism in West Germany, had suggested in 1954 that it join NATO, but this was rejected by the US.

The Soviet request to join NATO arose in the aftermath of the Berlin Conference of January–February 1954. Soviet foreign minister Molotov made proposals to have Germany reunified and elections for a pan-German government, under conditions of withdrawal of the four powers' armies and German neutrality, but all were refused by the other foreign ministers, Dulles (US), Eden (UK), and Bidault (France). Proposals for the reunification of Germany were nothing new: earlier on 20 March 1952, talks about a German reunification, initiated by the so-called 'Stalin Note', ended after the United Kingdom, France, and the United States insisted that a unified Germany should not be neutral and should be free to join the European Defence Community (EDC) and rearm. James Dunn (US), who met in Paris with Eden, Konrad Adenauer (West Germany), and Robert Schuman (France), affirmed that "the object should be to avoid discussion with the Russians and to press on the European Defense Community". According to John Gaddis, "there was little inclination in Western capitals to explore this offer" from the USSR, while historian Rolf Steininger asserts that Adenauer's conviction that "neutralization means sovietization", referring to the Soviet Union's policies towards Finland known as finlandization, was the main factor in the rejection of the Soviet proposals. Adenauer also feared that German unification might have resulted in the end of the CDU's leading political role in the West German Bundestag.

Consequently, Molotov, fearing that the EDC would be directed in the future against the USSR and "seeking to prevent the formation of groups of European States directed against the other European States", made a proposal for a General European Treaty on Collective Security in Europe "open to all European States without regard to their social systems", which would have included the unified Germany (thus rendering the EDC obsolete). But Eden, Dulles, and Bidault opposed the proposal.

One month later, the proposed European Treaty was rejected not only by supporters of the EDC, but also by Western opponents of the European Defence Community (like French Gaullist leader Gaston Palewski) who perceived it as "unacceptable in its present form because it excludes the USA from participation in the collective security system in Europe". The Soviets then decided to make a new proposal to the governments of the US, UK, and France to accept the participation of the US in the proposed General European Agreement. As another argument deployed against the Soviet proposal was that it was perceived by Western powers as "directed against the North Atlantic Pact and its liquidation", the Soviets decided to declare their "readiness to examine jointly with other interested parties the question of the participation of the USSR in the North Atlantic bloc", specifying that "the admittance of the USA into the General European Agreement should not be conditional on the three Western powers agreeing to the USSR joining the North Atlantic Pact". Again, all Soviet proposals, including the request to join NATO, were rejected by the UK, US, and French governments shortly after. Emblematic was the position of British General Hastings Ismay, a fierce supporter of NATO expansion. He opposed the request to join NATO made by the USSR in 1954 saying that "the Soviet request to join NATO is like an unrepentant burglar requesting to join the police force".