Book excerpt: At the Heart of the Borderlands is the first book-length study of Africans and Afro-descendants in the frontiers of Spanish America. While people of African descent have formed part of most borderlands histories, this study recognizes and explains their critical contribution to the formation of frontier spaces. Lack of imperial control coupled with Spain’s desperation for settlers and soldiers in frontier areas facilitated the social mobility of Afro-descendants. This need allowed African descendants to become not just members of borderland societies but leaders of it as well. They were essential actors in helping to shape the limits of the Spanish empire. Africans and Afro-descendants built, opposed, and shaped Spanish hegemony in the borderlands, taking on roles that would have been impossible or difficult in colonial centers due to the socio-racial hierarchy of imperial policies and practices.