While the previous chapter traced some of the intellectual developments that allowed for an articulation of Christianity with a commitment to revolutionary social change, the following three chapters will assess the formation and mobilisation of a movement of Christians identifying with social revolution. During the final years of the 1960s, liberationist Christianity consolidated into a broad-based socio-religious movement, adopting and generating a variety of concepts and forms of praxis. A determinate politico-religious culture was built, formulated in opposition to the Catholic Church's dominant practice and political alliances and in favour of a revolutionary socialist transformation of society. In this milieu, the dynamic relationship between religious faith and political principles became a defining characteristic of the liberationist Christian movement.

This chapter focuses especially on the central driving force of this movement: the Movement of Priests for the Third World (MSTM). The MSTM may be understood as a particular social movement organisation, which functioned to bring forward the claims, contentions and identity of the liberationist Christian movement. It was an organisation of Catholic priests that responded to both political and ecclesial developments in Argentina and internationally, the result of a concerted effort among Catholic priests from diverse backgrounds. This included spiritual advisors to the specialised branches of Catholic Action (JOC, JUC, JEC, MRAC); the worker-priests, who sought to undertake their priestly commitment fully immersed among the working classes and in poor neighbourhoods; clergymen who worked in academic environments, in universities or seminaries; and ordinary parish priests or members of religious orders.

The appearance of the MSTM in 1968, as well as with a more general radicalisation of Christians, should be understood within the context of General Juan Carlos Onganía's dictatorship initiated by the military coup d’état of 28 June 1966. Onganía, somewhat ironically given this disruption of constitutional order, was the figurehead of the so-called azul (blue) faction of the armed forces, associated with a concern for legality and constitutionalism. Following a series of confrontations in 1962 and 1963, the azules had prevailed over the colorado faction whose closer links to the more extreme sectors of Catholic nationalism and the far right underpinned a desire for a military government to declare all-out war on Peronists.