This essay tries to make a comparative analysis of the political dynamics of Portugal and Slovakia in the first half of the twentieth century (1910-1939) in terms of the significance of conservative political Catholicism. The two countries belonged to a group of nations in Europe in which there was a strong reaction to political liberalism, progressive republicanism, cultural secularism, and socialism. This antagonism can arguably be seen as a modern continuation of the historic conflict between the Protestant and humanist Reformation and the Catholic Counter-Reformation. Its twentieth-century manifestation was of course somewhat different from the original sixteenth- and seventeenth-century conflict. After the eighteenth century the historic force of anti-Catholic Reformation was mainly expressed in the form of intellectual Enlightenment, anti-clericalism, and social and cultural progressivism. But it would seem that in many ways the dynamics and aggressive energy of this great cultural confrontation was continued during the nineteenth and twentieth centuries, although in a modified ideological and political shape. The years between 1910 and 1940 were the period when the conflict between political progressivism and Catholic conservatism reached its culmination. In Portugal the forces of cultural secularism and liberal republicanism were defeated by the new authoritarian regime led by Salazar. In Slovakia the foundation and then the end of the First Czechoslovak Republic brought the rise and then the victory of the Catholic opposition movement, the Slovak People’s Party of Andrej Hlinka and Jozef Tiso. The authors of this essay would argue that a comparison of Portugal and Slovakia is useful in trying to understand the significance of the political force of conservative and anti-liberal Catholicism. From a Slovak point of view, looking at Portugal seems helpful in coming to terms with this European and Slovak phenomenon.