Mass dictatorship as a working hypothesis was designed to challenge the antithetical comparison of dictatorship and democracy inherent to the old school of totalitarian scholarship and the political common sense of the demonological dichotomy in the Cold War era. Initiated by the problematics of how to democratize democracy, the mass dictatorship thesis raises a set of questions: what if majoritarian democracy in the modern nation-state is based on the categorization of minorities as ``Others`` in terms of nation, class, gender, race, ethnicity and so on? What if the majority tyrannize minorities? Is that democracy or is it dictatorship? In answering these questions, it tries to comprehend the common ground between twentieth century mass dictatorships and mass democracies in their attempted mobilization of masses to participate voluntarily in and to support the regime. By locating the Holocaust in the context of the continuity of ``Western`` colonialism rather than by recourse to German peculiarities, the mass dictatorship thesis bridges between Western modernity and German peculiarity in perpetrating genocide. What I mean is not that dictatorship is the same as democracy, but that the dividing line is blurred much more than what was previously thought. That critical overview of the interwoven history of mass dictatorships and mass democracies in the twentieth century would lead us to a self-reflexive question of how to democratize democracies in the twenty first century.