San Ildefonso, Treaty of (1777)

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San Ildefonso, Treaty of (1777)

The Treaty of San Ildefonso (1777) was one in a series of agreements aimed at settling territorial disputes between Portugal and Spain regarding the interior of South America. On October 1, 1777, the Treaty of San Ildefonso ended fifteen years of irregular open fighting. The Portuguese regained Santa Catarina, seized by Spain in 1777, and the coastal Rio Grande area but acknowledged Spanish control of Colônia do Sacramento, a center of Portuguese contraband trade and an access to the silver mines of Potosí; the Seven Missions territory, occupied by seven Jesuit missions and thirty thousand Guaraní Indians; and the Banda Oriental (present-day Uruguay). Although neither power achieved its objective of complete control of what was known as the Debatable Lands, secret treaty provisions provided Spanish access to the Portuguese islands of Principe and São Tomé for the purpose of purchasing African slaves. Thus the Spanish gained direct access to the African slave market and circumvented the necessity of relying on foreign middlemen.

The Treaty of San Ildefonso was significant because it satisfactorily implemented the practical solution of recognizing that possession is the legal basis of territorial settlement (uti possidetis). This principle was originally agreed upon in the Treaty of Madrid (1750), but practical implementation of territorial allocation had been ignored since that treaty was nullified by the Treaty of El Pardo (1761).

In 1776 a Spanish expedition crossed the Río de la Plata and forcibly claimed a portion of what now is the southernmost territory of Brazil. The Treaty of San Ildefonso then recognized Spanish claims based on uti possidetis and inadvertently confirmed Portuguese claims to the Amazon basin, which was accepted as Brazilian territory because the Portuguese had explored, charted, and established permanent outposts there. The Spanish invasion of Portugal in 1801 prompted the Brazilian reconquest of portions of the contested area and reestablished the Chui River as Brazil's southern boundary. This was confirmed by the Treaty of Badajoz (1801), but the remainder of Brazil's territorial boundaries would not be settled until the twentieth century.

See alsoMadrid, Treaty of (1750) .


Dauril Alden, Royal Government in Colonial Brazil (1968), pp. 262-267, 474.

Geoffrey J. Walker, Spanish Politics and Imperial Trade, 1700–1789 (1979).

E. Bradford Burns, A History of Brazil (1980), pp. 70-72, 107, 146.

Peggy K. Liss, Atlantic Empires: The Network of Trade and Revolution, 1713–1826 (1983); The Cambridge History of Latin America, edited by Leslie Bethell, vol. 1 (1984), pp. 401, 473, 612.

Additional Bibliography

Torres, Simei Maria de Souza. Dominios y fronteras en la Amazonia colonial: El Tratado de San Ildefonso, 1777–1790. Fronteras de la Historia 8 (2003): 195-226.

                          Suzanne Hiles Burkholder

                                      Lesley R. Luster

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San Ildefonso, Treaty of (1777)

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San Ildefonso, Treaty of (1777)