The motivations of the characters in The Underdogs reflect the diversity of purposes behind those who took part in the Mexican Revolution. The novel was written while the revolution was still in progress, and reflects the chaos of the long struggle between various factions. While Emiliano Zapata was an ideological socialist, Pancho Villa was more pragmatic, fighting for personal loyalties and survival. It is in Villa's army that the protagonist, Demetrio Macías, rises to become a general. Even as a leader, however, Demetrio has no particular ideological commitment to the revolution. He confesses to Luis Cervantes that he does not understand politics, and he only joined the rebel army out of necessity in the first place.

Despite his lack of a political or ideological purpose, Demetrio is initially an inspiring leader, because there is a dignity in his courage and loyalty. There is a clear sense in which he is the purpose he does not understand, a peasant who wants to be able to live a decent life. His disillusion represents the failure of the revolution.

If Demetrio represents Pancho Villa's simple approach to the revolution, Luis Cervantes stands for a more cerebral, ideological approach. He sees the corruption of the government and wants to fight for what he sees as the alternative. It is perhaps surprising that, given his greater theoretical commitment to the revolution, Luis is not as thoroughly disillusioned as Demetrio. Even though he decides to leave Mexico, he does so with a sense that there is life and scope for optimism beyond revolutionary politics.

A character who illustrates another perspective and purpose is War Paint. She neither knows nor cares about politics, but profits from the war by seeking plunder. War Paint represents the self-interest of those on both sides who fight for personal gain.

The Underdogs presents the experiences of numerous characters involved in the Mexican Revolution in varied, highly distinct ways. Not only different parts of Mexican society, often from different areas of the country, but also different individuals had competing vested interests in the Revolution’s outcome. Even the federal troops changed loyalties among a rapidly changing array of presidents. With shifting coalitions, the joined opposition forces gradually gained strength. Several generals, notably Francisco (Pancho) Villa and Venustiano Carranza, led rival factions, while Emiliano Zapata aimed to unite the landless peasants. Throughout, the reader is often moved to wonder what people are fighting for, rather than fighting against. Conflicts arise as they switch sides, at times more from convenience than conviction. On the most fundamental level, the novel pits idealism against realism as Azuela paints revolution as a potential breeding ground for monsters.

Demetrio Macias is a peasant revolutionary fighter who moves from foot soldier to general. The progress of this natural leader through the Revolution’s battles and guerrilla fighting structures the novel. While Demetrio is sure that he and his fellow countrymen need a change, his motivations stem in part from his deep sense of personal injustice. Persecuted by the federal troops, who burn down his house, he commits to opposing them to the death. Yet he admits that fighting is as much a way of life as means to an end, stating that he can no more stop fighting than a pebble tossed into a canyon can stop falling.

In contrast, Luis Cervantes is an urban elite and apparently an unwilling recruit to the rebel cause. A former medical student, his motivation lies in rejection of the corruption of the establishment and upper classes. While the daily hardships and moral quandaries of battle erode his idealism further, he nonetheless attempts to infuse Demetrio with belief in the nobility of the cause. As Luis loses confidence that the revolution can succeed, his attitude becomes more pragmatic and he indulges in illegal behavior.

Demetrio’s followers rarely seem devoted to the ideals of social justice. Their interactions degenerate into personal feuds that undermine their effectiveness as a fighting force and push them to the brink of anarchy. Margarito in particular seems not merely amoral but sadistic.

Gender also structures the characters’ attitudes. Asturias generally presents the motivations of the female characters as personal, even to the point of apolitical. Camilla, who participates as a nurse for the rebel troops, is at first attracted to Luis but later torn by her affection for Demetrio. Another woman, La Pintada, becomes obsessed with jealousy over Demtrio and ultimately murders Camilla.

One of the brilliant aspects of this text is the way in which the supposedly pure ideal of the revolution is shown in its reality as the revolutionaries engage in more and more random and meaningless acts of violence. This demonstrates the understanding and view that Demetrio and the other revolutionaries have of human life. What starts off as a cause that is carried out against Federal troops and what they stand for quickly descends into something much more primitive brutal and disturbing.

Azuela seems to use this to point out the way in which fighting for a supposed "cause," such as an independent Mexico, actually serves as a front or a guise for the ability to express more primitive and base emotions. Note the way in which the so-called "heroes" of the revolution who outwardly state they are fighting for their country slowly begin to kill without rhyme or reason. Initially, the murders they commit are justified, but later on, all attempts of trying to justify their actions are abandoned. For example, Blondie ties a rope around a dead soldier's neck and drags it behind his horse and a priest is executed for the crime of wearing city clothes. As the novel continues, each act of violence becomes more and more meaningless, showing that the cause of the revolution only serves as a "front" to demonstrate the true brutal nature of man.