As in Europe, secular nation building in Latin America challenged the traditional authority of the Roman Catholic Church in the early twentieth century. In response, Catholic social and political movements sought to contest state-led secularisation and provide an answer to the 'social question', the complex set of problems associated with urbanisation, industrialisation, and poverty. As Catholics mobilised against the secular threat, they also struggled with each other to define the proper role of the Church in the public sphere. This study utilizes recently opened files at the Vatican pertaining to Mexico's post-revolutionary Church-state conflict known as the Cristero Rebellion (1926-1929). However, looking beyond Mexico's exceptional case, the work employs a transnational framework, enabling a better understanding of the supranational relationship between Latin American Catholic activists and the Vatican. To capture this world historical context, Andes compares Mexico to Chile's own experience of religious conflict. Unlike past scholarship, which has focused almost exclusively on local conditions, Andes seeks to answer how diverse national visions of Catholicism responded to papal attempts to centralize its authority and universalize Church practices worldwide.The Politics of Transnational Catholicism applies research on the interwar papacy, which is almost exclusively European in outlook, to a Latin American context. The national cases presented illuminate how Catholicism shaped public life in Latin America as the Vatican sought to define Catholic participation in Mexican and Chilean national politics. It reveals that Catholic activism directly influenced the development of new political movements such as Christian Democracy, which remained central to political life in the region for the remainder of the twentieth century.