One of the ideas put forth by the cartel thesis is that political parties in power cartelize the system by regulating parties in a way as to preserve their own survival. The thesis argues that despite their differences cartel parties act in unison in order to prevent new joiners of the club by structuring institutions such as state subventions and ballot access in ways that disadvantage challengers. Yet, new political parties continue to appear and successfully enter parliament which suggests that ruptures can emerge in a cartel. So far however, with only few exceptions, studies concerned with this aspect of the party cartel theory have failed to systematically explore what constitutes cartelization and whether a cartel can be broken. Using comparative parliamentary data and a newly-built dataset on party regulation in post-war Europe, we explore rules affecting party entry and party formation over time and show that while parties are more regulated today than they were before, the relationship between regulation and party entry does not hold.
