4 ideas
He rises to general under Villa's banner, then loses his footing when the revolutionary factions split. Near the end his wife asks why he keeps fighting, and he tosses a stone into a canyon and answers, 'Look at that stone, how it keeps on going.' He dies in the same canyon where his first victory took place, still firing his rifle.
Men who take up arms over a concrete personal grievance keep fighting long after that grievance is settled or forgotten. Momentum, habit, and the loss of any other life to return to take the place of purpose. Once war becomes a way of living, asking 'why fight?' has no answer beyond the fighting itself.
The educated recruit Luis Cervantes joins the band speaking of ideals and 'the cause.' He uses that rhetoric to flatter the illiterate leader and to steer the looting toward his own gain, then escapes to comfort in the United States. The lens is that the people who articulate a revolution's ideology are often the ones best placed to profit from it and to leave it. The people who do the fighting and dying cannot describe what they are fighting for.
The band starts with defensive, grievance-driven violence. Each easy success makes looting, drunkenness, and cruelty more routine, and the fighters come to resemble the federal troops they first resisted. Characters like the killer Margarito and the camp follower Pintada show where this drift ends.