|Hold it right there, outlaw!|
This article is littered with spoilers, so I reckon you might ought'a mosey on down the road if you don't want to read any plot details.
The Mexican Revolution was an outbreak that happened because of discontent among the lower social classes such as peasants with the tyrannical rule of General Ignacio Sanchez. The revolution began in the Mexico province of Nuevo Paraiso and was led by Abraham Reyes, who claimed he would improve the conditions of the workers and restore Mexico in to a democracy run by the people. His charisma allowed him to be an excellent recruiter to his cause. The Mexican government was quick to send an army to quell any uprisings, and trusted all of the reinforcements in Nuevo Paraiso to the provincial governor Colonel Agustin Allende.
The Mexican Army won some battles, and also massacred rebels and civilians to serve as an example, but the army couldn't stop the quick growth of the revolution supporters (such as John Marston, who helped the revolution in numerous assaults). And lost much of its leaders like Espinoza and De Santa. The army lost most of its strongholds to rebels such as the fort of El Presidio and the town of Escalera, which was home to Allende and a stronghold of the Mexican Army, was attacked and taken over by the rebels.
Allende was not a popular leader, and tried to flee, but was caught and executed by Reyes (or Marston). Later the rebels marched to Mexico City, and after a bloody battle, they won the war and overthrew Sanchez's government. Sanchez was presumably killed or fled in to exile. It is stated that the casualties were very large, rounding the number to 10,000 deaths. Reyes then assumed the position as the new president of Mexico, and promises to return Mexico to a democracy. However, it is stated in a newspaper in 1914 that Reyes is still the president and became a tyrant, proving he was no better than Sanchez was.