The Cristero war was a direct result of the Mexican constitution in 1917. This was a revolution that was fought over the enforcement of anti-clerical laws. This uprising took place during the Plutarco Elias Calles presidency. He began to enforce the parts of the constitution that outlawed Catholicism in Mexico as well as adding the Calles Laws which further enforced the laws of the constitution. This was an extremely bloody war as around 250,000 people were killed during the short conflict. To this day Catholicism plays a vital role in Mexico, as over 80 percent of the population identify as Catholic. The war ended in 1929 because of an agreement between the church and government, but this didn't come with any change to the written law, just how it was informed. The written change didn't happen until much later.

Source:  Rendon, Andres. “The Cristero War and Mexican History.” HistoricalMX, historicalmx.org/items/show/128.