Upon his controversial and successful publication of Words of a Believer (1834), Lamennais became one of the most influential thinkers in Europe and America. Lamennais's other works, such as Modern Slavery, have received surprisingly less attention, considering that with it he made a re-description of the concept people and consequently of democracy. Lamennais's presentation of the antagonism between liberty and tyranny, between a few oppressors (privileged classes) and the majority of the oppressed (the people) turned him into a key reference for the democratic, republican, and socialist political cultures. We can then speak of a “Lamennais moment” as opposed to the “Guizot moment,” which offered conflicting world views. This article combines an analysis of the translations and circulation of Modern Slavery in Spain and Latin America with the study of the new meanings of the concept people.