Summary

This work considers the Acre War as part of a multilateral context where the balance of power was important in the reasoning behind the establishment of foreign relations. It uses the frontier concept developed by FJ Turner to explain why their open border put Brazil and Bolivia in confrontation. This happened because of the Bolivian strategy of granting land to investors from the United States, Great Britain and France, which was interpreted by Brazil as an imperialist action promoted by the United States. This explains why Brazil established a close relationship with Chile to confront together their problems in Acre and Antofagasta, which led to the drafting of the Petrópilis (1903) and Paz y Amistad (1904) treaties. The article argues that Bolivia proceeded this way to avoid a Brazilian, Peruvian or Paraguayan territorial advance, seeking the support of the United States to compensate the imbalance of power.