Wikipedia:

The Cristero War (also known as the Cristiada) of 1926 to 1929 was an uprising and counter-revolution against the Marxist Mexican government in power at that time. The rebellion was set off by the persecution of Roman Catholics and specifically the strict enforcement of the anti-clerical provisions of the Mexican Constitution of 1917 and the further expansion of anti-clerical laws. After a period of peaceful resistance, a number of skirmishes took place in 1926. The formal rebellions began on 2 January 1927, with the rebels called Cristeros because they felt they were fighting for “Cristo Rey” (“Christ the King”). The rebellion ended by diplomatic means brokered by the then United States Ambassador to Mexico, Dwight Whitney Morrow.

New trailer for Cristeros film