South America 1865: Paraguayan Offensives

When its war with Brazil began in December 1864, Paraguay swiftly overran southern Mato Grosso. However, to reach its Uruguayan allies, Paraguay needed to move through Argentina. When Argentina refused access, the Paraguayans invaded but were still too late to stop Brazil overthrowing the Uruguayan government. In May 1865, Brazil, Argentina, and Uruguay formed the Triple Alliance to defeat Paraguay.



Patagonia was regarded as terra nullius by Britain and France until 1881 (and thus shown as a separate state in most maps of the period). Their main concern, shared with the United States, was to prevent any nation restricting navigation through the Straits of Magellan.

Main Events

14 Dec 1864–1 Aug 1868 Mato Grosso Campaign

In December 1864, 3,200 Paraguayan troops advanced upriver into Mato Grosso province, Brazil, capturing the river fort of Nova Coimbra and moving as far inland as Corumbá and the Mandioré lagoon. Meanwhile an eastern Parguayan column of 3,500 pushed inland and by river to capture Dourados and, in April 1865, Coxim. The Brazilian response was slow and suffered numerous setbacks; the last Paraguayan troops only withdrew from Mato Grosso in 1868 after the Allies invaded Paraguay from the wikipedia

27 Jan 1865 Vivanco-Pareja Treaty

Peru and Spain signed the Vivanco–Pareja Treaty on board the frigate Villa de Madrid to further cooperation between the two countries in the wake of the Spanish occupation of the Chincha Islands. However, this action discredited Peruvian President Juan Antonio Pezet, who was seen as weak in the face of Spanish aggression, and opposition to the treaty would help bring about his overthrow by the end of the wikipedia

29 Mar 1865 Paraguay at war with Argentina

On 14 January 1865, Paraguay requested Argentine permission to move troops troops through Misiones District to attack the Brazilian province of Rio Grande do Sul. Argentina—which had previously rejected a similar Brazilian request—refused, prompting the Paraguayan Congress to authorize hostilities on 18 March. President Solano López declared war that day, although the declaration would not be published until the 23rd and would only be sent to the Argentine government on the 29th. Argentina officially received the declaration on 3 May, responding in kind six days wikipedia

13 Apr–5 Aug 1865 Invasion of Corrientes

Paraguayan forces crossed into Argentina, seizing the city of Corrientes on 14 April 1865 and pushing south down the Paraná River to reach as far as Goya. In the east, two Paraguayan columns advanced down either side of the Uruguay River, capturing Paso de los Libres (Argentina) and Uruguaiana (Brazil). Although initially unable to match Paraguay’s military, Argentina and Brazil were more successful at contesting the invasion with their river navies; in late May they even briefly recaptured Corrientes with a river-borne wikipedia

1 May 1865 Treaty of the Triple Alliance

The foreign ministers of Argentina, Brazil, and Uruguay signed the Treaty of the Triple Alliance in Buenos Aires. The treaty allied the three countries in their war against Paraguay, prescribed how the war would be conducted and outlined post-war settlements. At the insistence of Brazilian envoy Francisco Octaviano—and despite Argentine opposition—the treaty also guaranteed Paraguay’s long-term wikipedia

9 May 1865 Johnson’s May 9 Declaration

The United States President Andrew Johnson declared that armed resistance in the American Civil War was “virtually” at an end and that nations or ships still harboring fugitives would be denied entry into US ports. Confederate President Jefferson Davis was captured the following day, although it would not be until 20 August 1866 that Johnson would formally proclaim the end of the wikipedia

11 Jun 1865 Battle of the Riachuelo

Two Paraguayan steel corvettes, six steamers, and some barges under the command of Pedro Ignacio Meza attempted to launch a surprise attack on the Brazilian fleet, anchored near Riachuelo Creek to the south of Corrientes, Argentina. However, mechanical difficulties delayed the assault, allowing the Brazilian force—one steel frigate, four corvettes, and four gunboats under Francisco Barroso, Baron of Amazonas—to fight off the offensive over the course of a day, sinking or capturing eight boats for the loss of one. The battle was a decisive victory for the Triple Alliance, effectively giving it control of the Plate river system south of wikipedia