As the Spanish empire expanded, the growing abundance of horses elevated an underlying tension between two colonial goals: to populate land with horses bred in new settlements, and to control land in new settlements by regulating the movement, reproduction, and possession of horses in them. The horse population increased due to both evolutionary environmental affinities and the use of traditional husbandry methods, such as loose herd management and protection of the commons, which had some unintended consequences. The responses of Spanish and Indigenous actors to these changes presented opportunities to negotiate the perception of and exercise of Spanish imperial power in a new equine political ecology.