1968: Student Revolution
European and American IMCS federations were greatly impacted by the May 1968 Revolution at the University of Pars and the anti-Vietnam War movements. Many students were empowered by these events, but sadly some of the national movements experienced a sharp decline.

1960s and 1970s: Liberation Theology
In the 1960s and 1970s, IMCS, inspired by the Vatican Council, regional bishops meetings, the major social encyclicals and the experiences of its members, focused its attention on the poor and the marginalized.

At this time, IMCS in Latin America was growing closer to IYCS. A number of IMCS federations were in fact YCS groups in the university and were double affiliated to both. In Latin America, the two movements worked very closely and took leading roles in Liberation Theology. Former IMCS member and Chaplain of IMCS Peru (UNEC), Fr. Gustavo Gutierrez, OP would have a significant impact on IMCS, the Church, and the world (especially Latin America) with the writing of "A Theology of Liberation" (1971). This foundational text of Liberation Theology references IMCS, IMCS national movements and members several times.

A significant moment in IMCS occurred in the 1971 IFA in Fribourg. While celebrating IMCS' 50^th anniversary, this 27^th IFA focused on "Liberation - How?" This IFA changed the methods in which IMCS held international meetings. Instead of hearing from eminent personalities and then having student workshops, the 1971 IFA began with the student experience and held study sessions in methods drawing from the Catholic Action methods.

The next IMCS IFA would take place in Lima in August of 1975 with 80 delegates coming from 32 national federations. This IFA used the same methodology as in 1971 and focused on the theme "Christian Commitment in a world in crisis." This meeting reexamined the role and life of IMCS and committed itself to the preferential option for the poor.

IMCS would also impact Liberation Theology in the Asian context with Tissa Balasuriya, O.M.I of Sri Lanka serving as an active chaplain to IMCS at the local and regional level.