Boundary treaty of 1881 between Chile and Argentina

The Boundary Treaty of 1881 (Spanish: Tratado de Límites de 1881) between Argentina and Chile was signed on the 23 July 1881 in Buenos Aires by Bernardo de Irigoyen, on the part of Argentina, and Francisco de Borja Echeverría, on the part of Chile, with the aim to establish a precise and exact borderline between the two countries based on the uti possidetis juris principle. Despite dividing largely unexplored lands this treaty laid the groundwork for nearly all of Chile's and Argentina's current 5600 km of shared borders.

Argentina declared its independence in 1816 and Chile did the same in 1818. Once the Spaniards had been expelled, relations between the two nations soured primarily due to a border dispute: both claimed to have inherited overlapping parts of Patagonia.

The Chilean constitution of 1833 established the Andes as its eastern boundary. This view of Chile's borders was challenged in 1853 by Miguel Luis Amunategui's book Titles of the Republic of Chile to Sovereignty and Dominion of the Extreme South of the American Continent, on which he put forward that Chile had valid arguments to claim all of Patagonia.[1] These claims traced Chilean claims back to the conquest of Chile in the 16th century by Pedro de Valdivia, arguing that Pedro de Valdivia obtained rights from the Spanish crown to establish a captaincy limited by the Strait of Magellan to the south. Pedro de Valdivia subsequently founded several cities through southern Chile with the goal of reaching the Strait of Magellan. However the remoteness of the region and the Mapuche in the War of Arauco limited further expansion to the south.

The Republic of Chile founded Fuerte Bulnes in 1843, and later Punta Arenas in 1847, giving a strong impulse to steam navigation through the Strait of Magellan and probably averted the occupation of the strategically crucial strait by the European powers or the United States. As stated by Michael Morris in "The Strait of Magellan":

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