This thesis is a comparative study of three communist party national conferences held in the Soviet Union, Hungary and Yugoslavia between May and June 1955. New evidence, from archival materials and interviews conducted in these countries, shows how the conferences were convened in consonance with one another and how actors in these states collaborated for the purpose of modernising their respective parties with a view to rebuilding the party's legitimacy and maintaining the one-party state.

This dissertation analyses the process of the disintegration of the Communist Party of the Soviet Union (CPSU), which is central to the Soviet collapse. The disintegration process also provides a good opportunity to test existing theories of political regime change. In terms of source use, this dissertation makes extensive use of the party archives that became available after the Soviet collapse. This makes possible a very detailed analysis of work of the party apparat. The importance of the subject and a review of existing theories that offers some hypotheses are discussed in the first chapter. In the second chapter, the reason why the party reform was necessary is considered through analysing the situation within the party before the perestroika period. The analysis makes clear that the CPSU faced a dilemma between monolithic unity and monopolistic control before the perestroika period, which made party reforms necessary. The third chapter deals with party-state relations under Gorbachev’s reform in detail. This chapter discusses the fact that, as a result of the reorganisation of the party apparat that was intended to stop the party’s interfering in the state body, the party lost its traditional administrative functions. This, however, led to a ‘power vacuum’ because no other alternative power centre was established quickly, and complicated further reform attempts. Moreover, the party failed to find a new function as a ‘political party’, as considered in detail in the fourth chapter. Despite attempts at competitive party elections and the emergence of party platforms, Gorbachev failed to transform the CPSU into a ‘parliamentary’ rather than a ‘vanguard party’. Therefore, the CPSU lost its raison d’être, which accelerated a mass exodus of members. The rapid decline in party membership caused a financial crisis which is considered in the fifth chapter. The financial crisis and the soviets’ demands for the nationalisation of party property forced the CPSU to engage in commercial activity. Nonetheless, commercial activity unintentionally caused the fragmentation or dispersal of party property. On the other hand, the ‘power vacuum’ expanded so much that some emergency measures seemed necessary to some top state leaders. The August attempted coup is discussed in the sixth chapter in the context of party-military relations. When Russian president Yeltsin suspended its activity, the CPSU had lost its raison d’être and its property had been fragmented or dispersed. Thus, the CPSU had no choice but to accept the reality that it was ‘dead’ de facto. The final chapter gives an overview of this pattern of developments, and compares it with the experiences of other communist parties’ reforms in East Europe. The theoretical implications are also considered in the final chapter, which argues that existing theories of political regime change are not sufficient and that a further effort of conceptualisation based on the realities considered in the thesis is necessary.