Between February 1868 and September 1870, 7 contingents totalling 507 Canadians enrolled in the papal army (whose soldiers were known as Papal Zouaves) to help defend Rome from the Italian troops who wanted to bring about Italian unification. The last contingent of 114 recruits left too late and had to turn back, for Rome surrendered on September 20.

Most of the Canadian Zouaves were educated young men recruited in Québec. The organizational committee set up by Bishop Ignace Bourget of Montréal had recruited them for their moral qualities, because the main goal was to create an elite able to oppose the propagation within Québec of liberal ideas formally condemned by the pope. For this reason, care was also taken to ensure that every parish provided volunteers and financial support. Freedom of speech and conscience, popular sovereignty and the separation of church from state - such were the grand ideals that the Zouaves were to combat. Upon their return from Rome, they formed an association whose goal was to promote the cause they had defended by arms. At the end of the century, with the Catholic Church becoming reconciled with the modern world, the Zouaves' association adapted its objectives to the concerns of Catholic action groups. The association still exists, but its influence is very limited.