In South America , the Portuguese conquered from Spain most of the Rio Negro valley, and repelled a Spanish attack on Mato Grosso . Between September 1762 and April 1763, Spanish forces led by don Pedro Antonio de Cevallos, Governor of Buenos Aires  undertook a campaign against the Portuguese in Uruguay and South Brazil. The Spaniards conquered the Portuguese territories of Colonia do Sacramento and Rio Grande de São Pedro and forced the Portuguese to surrender and retreat. Under the Treaty of Paris , Spain had to return to Portugal the colony of Sacramento, while the vast and rich territory of the so-called "Continent of S. Peter"  would be retaken from the Spanish army during the undeclared Hispano-Portuguese war of 1763-1777. As consequence of the war the Valdivian Fort System, a Spanish defensive complex in southern Chile, was updated and reinforced from 1764 onwards. Other vulnerable localities of colonial Chile such as Chiloé Archipelago, Concepción, Juan Fernández Islands and Valparaíso were also made ready for an eventual English attack.. What was the latter 1/10 of a decade that Spanish forces led a campaign against the Portuguese in Uruguay and South Brazil?