Written in 1915, this is considered one of the great novels of the Mexican Revolution. It draws on his experiences as a doctor in the Revolutionary Army, which, in his telling, is less an army than a ragtag guerrilla group that devolves into a predatory gang, looting and killing sheerly for the hell of it.
There's very little politics involved. It's about the personalities of the gang, especially Demetrio Macias, a peasant who becomes a "general" in Pancho Villa's Army through fearlessness and instinctive military skill. A couple of city slickers in the beginning are able to articulate some ideals for the revolution, but by the end of the novel the fighting is nihilistic. It's more brutal than any spaghetti western you've ever seen.
The characters, though sketched in stark strokes, are vivid and memorable, especially a fierce female fighter, (called in this translation War Paint), and the pensive Demetrio.
Although Azuela was sympathetic to the initial goals of the uprising, this is a dire warning to anyone who romanticizes revolution. Once the demon of violence is unloosed, it is the most ruthless who ride the chaos to power.