The Cristero War was a widespread struggle in central and western Mexico from 1 August 1926 to 21 June 1929 in response to the implementation of secularist and anticlerical articles of the 1917 Constitution. The rebellion was instigated as a response to an executive decree by Mexican President Plutarco Elías Calles to strictly enforce Article 130 of the Constitution, a decision known as Calles Law. Calles sought to eliminate the power of the Catholic Church in Mexico, its affiliated organizations and to suppress popular religiosity.

The rural uprising in north-central Mexico was tacitly supported by the Church hierarchy, and was aided by urban Catholic supporters. The Mexican Army received support from the United States. American Ambassador Dwight Morrow brokered negotiations between the Calles government and the Church. The government made some concessions, the Church withdrew its support for the Cristero fighters, and the conflict ended in 1929. The rebellion has been variously interpreted as a major event in the struggle between church and state that dates back to the 19th century with the War of Reform, as the last major peasant uprising in Mexico after the end of the military phase of the Mexican Revolution in 1920, and as a counter-revolutionary uprising by prosperous peasants and urban elites against the revolution's rural and agrarian reforms.