The crisis in relations with Czechoslovakia, arose in 1968, was one of the most acute foreign policy problems for the Soviet Union and its Warsaw Pact allies. The author of the article, which is based on declassified documents, including the ones of the Politburo of the CPSU Central Committee, showed that the USSR authorities and their East European allies were seriously afraid that the reforms launched in Czechoslovakia would open the prospect of the departure from socialism and the subsequent withdrawal of the country from the Warsaw Pact. The anti-socialist and anti-Soviet forces that were openly operating there were of particular concern. The leaders of the USSR, especially L.I. Brezhnev, sought to resolve this acute situation through political compromises with Czechoslovak side and its fulfi llment of the commitments made during the multilateral meetings. Initially they avoided a military intervention in Czechoslovakia, which was insisted upon by the allies of the Soviet Union, the members of the ATS, i.e., Poland, GDR, Bulgaria, and Hungary. However, the Czechoslovak leaders, A. Dubček in the first place, did not comply with the reached agreements (in particular, stoppping the anti-Soviet media campaign and personnel changes), although this could have prevented the entry of troops. By August 1968, the possibilities of getting out of the situation by political means had been exhausted. Not only the five Warsaw Pact countries were responsible for the invasion, but also the leaders of Czechoslovakia. The USSR and the other ATS countries were guided by the motive of saving socialism in Czechoslovakia and its preservation as part of the Warsaw Pact when making the decision to send in troops. The ATS unity during the Cold War made it possible to ensure the balance of power with the NATO on the European continent. The theoretical justifi cation of the right to interfere in the aff airs of one or another country of the socialist commonwealth by other socialist countries to save socialism was given aft er the entry of troops. In the West, this policy will become known as the “Brezhnev Doctrine”.