BATTLE // June 10, 1865
Invasion of Rio Grande do Sul
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Overview
The invasion of Rio Grande do Sul began on 10 June 1865 when about 7,500 soldiers under the command of General Antonio de la Cruz Estigarribia invaded the village of São Borja near Brazil's border with Argentina. About 3,000 men commanded by Major Pedro Duarte stayed on the other side of the Uruguay River to accompany the advance of the main column. The Paraguayans always advanced along the river without major damage, with the exception of a confrontation on the Butuí River where a Paraguayan battalion had been defeated, until they reached Uruguaiana, where a two-month siege made them surrender unconditionally on September 18. The main objective of Paraguayan president Francisco Solano López to invade Rio Grande do Sul was to force a peace treaty favorable to the Paraguayans with the Empire of Brazil. The action took place in the second phase of the Paraguayan War, known as the Corrientes campaign.
Overview adapted from Wikipedia, licensed under CC BY-SA 4.0.
Significance
The Paraguayan invasion of Rio Grande do Sul in June 1865 was a strategic offensive ordered by President Francisco Solano López with the aim of compelling the Empire of Brazil to negotiate a peace settlement on terms favorable to Paraguay. Estigarribia led approximately 7,500 troops across the Uruguay River into São Borja, while a secondary force of roughly 3,000 men under Pedro Duarte provided flank support along the river. Despite advancing through Brazilian territory with limited initial resistance—suffering only a localized defeat at the Butuí River—the campaign culminated in a two-month siege at Uruguaiana that ended with the unconditional surrender of the Paraguayan force on September 18. Paraguayan casualties reached approximately 5,500. The operation failed to extract the diplomatic concessions López sought and instead demonstrated the limits of Paraguayan power projection beyond its own borders. The episode formed part of the broader Corrientes campaign, the second phase of the Paraguayan War, and the surrender at Uruguaiana effectively ended Paraguay's offensive initiative on the southern front.
Tactics
Estigarribia's force advanced along the Uruguay River, using the waterway as a logistical and navigational axis. A secondary column of roughly 3,000 men under Duarte remained on the opposite bank to accompany and support the main column's progress. The Paraguayans encountered minimal resistance along the river route, with the exception of a defeat sustained by one battalion at the Butuí River. The advance concluded at Uruguaiana, where the force was subjected to a siege lasting approximately two months before surrendering unconditionally.
Forces & casualties
Troop strength
- Empire of Brazil14,000–17,000medium
- Paraguay10,000–12,000medium
Empire of Brazil fielded a 1.4 : 1 numerical advantage
Casualties
- Paraguay5,500medium50% loss rate
Commanders (7)
Empire of Brazil



Marques de Sousalieutenant general
Paraguay
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