Context: One such move, in regard to land reform, was to nationalize most farmland and give it to the peasants across Mexico. He also put into effect a national school system that was largely secular to combat church influence in late 1924. After two years the church protested the movement by refusing to give the blessed sacrament to the populace. Some peasants also joined in the protests, adding greater land reforms to the list of demands by the rebelling priests. The rebellion was openly supported by the Catholic Church and received funding, beginning the Cristero War. Meanwhile, in 1927, another military coup was attempted, this time receiving support from land owners. Calles quickly crushed the rebellion with help from the newly mobilized peasant battalions, who later on were used to fight against the Church. In the midst of the mobilized worker's militias, land reform, and anti-church actions, the American government began to openly declare Mexico a Bolshevik regime. To recover from the backlash, Calles began to tone down the radical rhetoric and slowed land reform policies in 1928. A year later, Calles defeated the church ending the rebellion. After the war ended in 1929, supporters of Calles and Obregón began to form a united political party called the National Revolutionary Party or PNR. This was to unite the various revolutionary factions of the civil war to prevent further Cristero revolts and build stability. After a series of interim presidents controlled by the party, Lázaro Cárdenas took power in 1934. Cárdenas was a socialist and began to base government policy on class struggle and empowering the masses. However, not all of his reforms were completely socialist, making him somewhat more centrist than purely socialist. Regardless, his rule was the most radical phase of the post revolution, social revolution.

Question: When did the Cristero War begin?

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