In the second half of the last century, the labor movement introduced an important innovation in political organization by founding mass workers' parties. Conditions of illegal struggle by the working class led, at the beginning of this century, to the formation of still another type of labor party. This is Lenin's cadre party, later to be called communist parties. As for the one-party system, it can be said in general that it has all the negative characteristics of multiparty systems without their positive characteristics. The bureaucratic mentality has begun to check the activity of the League of Communists as the social avant-garde. Bringing the bureaucratic processes under control was made possible by two factors: consolidation of the Yugoslav social system on a basis of self-government, and establishment of the possibility of continual comparison of self-governing and bureaucratic activities. If criticism is lacking, the process of bureaucratization and hierarchical structuring of society takes place.