This article aims to study the work of Chilean historian Diego Barros Arana on the Mapuche people through a historical analysis of primary and secondary sources. It is based on the premise that his work analyzes the Mapuche people, focusing on their inclusion or exclusion within the nation-state. This study reveals that his work developed under a discursive tension between safeguarding the warrior image of the Mapuche, characteristic of the colonial period, and, on the other hand, describing them as a people in decline, as they were perceived in the 19th century. Finally, the Chilean historian's vision of the Mapuche people, with all his contributions, was based on the conceptions of his time and shaped the image that prevailed in Chilean society during the 20th century.