The monograph explores the complex problems of transforming the political regimes of Eastern Europe in the second half of the 20th century. It deals with a wide range of issues in the political history of Eastern Europe: the concept of transforming the regimes of popular democracy into unified political systems; the role of the Soviet factor in the fate of Eastern European countries; the socio-political nature of the controversy; crises; the origins and mechanisms of the disintegration of the omnipotence of the ruling parties; attempts to modernize regimes and the political struggle of social forces, which resulted in a "gentle" revolution; formalizing the structures of a new democratic political system.