The most important theme that runs through Las Casas’s work is also its reason for existing: The genocide Spanish colonists committed against the indigenous peoples of South America. Each chapter details acts of incredible brutality by the Spanish against the largely defenseless peoples of the New World, with no provocation from this indigenous group. These acts of atrocity include massacring villages, burning people alive, feeding people to dogs, throwing people off mountains, disfiguring and dismembering children, raping women, and countless other violent acts. Las Casas maintains an unflinching gaze toward these atrocities, documenting them in a historically useful level of detail. Las Casas approaches these acts from a position of moral disbelief, repeatedly admitting that it is impossible to detail the true horror of these events. That said, the death tolls reported by Las Casas should not be interpreted as wholly accurate. In other works Las Casas is careful to mention that the number of causalities is meant to give the reader a sense of these atrocities, not an exact count of the dead.

Las Casas’s reasons for actively petitioning for the abolition of these acts are twofold. First, as we get a sense of in the text, Las Casas is a true humanitarian who objects to the massacre of innocent indigenous people simply because it is cruel.