This theme is devoted to the period which can be called "the apogee of the socialist experiment". The main objective of the study — to research the causes of the failure of the USSR in strategic civilizational competition with the West. The paper discusses the problems of political, economic and social development of the Soviet Union in the postwar period, as well as the major foreign policy challenges and problems faced by the Soviet Union in those years. The final part of the study is devoted to an attempt to modernize Soviet society and the state in the course of "perestroika" policy and the process of disintegration of Soviet Union.