The Boundary Treaty of 1866 between Chile and Bolivia, also called the Mutual Benefits Treaty, was signed in Santiago de Chile on August 10, 1866, by the Chilean Foreign Affairs Minister Álvaro Covarrubias and the Bolivian Plenipotentiary in Santiago Juan R. Muñoz Cabrera. It drew, for the first time, the border between both countries at the 24° South parallel from the Pacific Ocean to the eastern border of Chile and defined a zone of bipartite tax collection, the "Mutual Benefits zone", and tax preferences for articles from Bolivia and Chile.
Despite increasing border tensions since the 1840s, both countries fought together against Spain in the Chincha Islands War (1864–65) and resolved the question under the Governments of Mariano Melgarejo in Bolivia and José Joaquín Pérez in Chile. But before long, both countries were discontented with it, and Peru and Bolivia signed a secret treaty against Chile in 1873. The Lindsay-Corral protocol, thought to clarify the treaty, was approved by Chile but never by Bolivia.
