What is the theme in The Underdogs a Novel of the Mexican Revolution by Mariano Azuela?

One of the main themes of the book is the nature of Demetrio's men and the rebel cause in general during the Mexican Revolution. At the beginning of the book they are hailed as heroes in the towns where they arrive. Everyone has a hatred of the Federals; Federals, or so is the perception, are the ones who force men unwillingly into its armies, who loot indiscriminately, and who kidnap daughters and wives, and it is the rebels who fight heroically for the people against tyranny.