The guerrilla war lasted for 14 months until president Francisco Solano López was killed in action by Brazilian forces in the Battle of Cerro Corá on 1 March 1870.

The territorial disputes became worse when the Viceroyalty of the Río de la Plata collapsed in the early 1810s, leading to the rise of Argentina, Paraguay, Bolivia, and Uruguay.

[8][9] In the case of Paraguay and Brazil, the problem was to define whether the Apa or Branco rivers should represent their actual boundary, a persistent issue that had confused Spain and Portugal in the late 18th century.

Paraguay had recurring boundary disputes and tariff issues with Argentina and Brazil for many years during the rule of Solano Lopez's predecessor and father, Carlos Antonio López.

As no roads linked the inland province of Mato Grosso to Rio de Janeiro, Brazilian ships needed to travel through Paraguayan territory, going up the Paraguay River to arrive at Cuiabá.

[18] Brazilian soldiers on the northern borders of Uruguay started to provide help to Flores' troops and harassed Uruguayan officers, while the Imperial Fleet pressed hard on Montevideo.

On 12 November Tacuarí caught up with Marquês de Olinda in the vicinity of Concepción, fired across her bows, and ordered her to return to Asunción; when she arrived on the 13th, all on board were arrested.

[26][27] However, public opinion quickly changed for the worse when newspapers began running stories painting the convention of 20 February as harmful to Brazilian interests, for which the cabinet was blamed.

Not only had Paranhos managed to settle all Brazilian claims, but by preventing the death of thousands, he gained a willing and grateful Uruguayan ally instead of a dubious and resentful one, which provided Brazil with an important base of operations during the acute clash with Paraguay that shortly ensued.

A column of 2,780 men led by Manuel Pedro Drago left Uberaba in Minas Gerais in April 1865 and arrived at Coxim in December, after a difficult march of more than 2,000 kilometres (1,200 mi) through four provinces.

[16]: 30 Along with Robles' troops, a force of 12,000 soldiers under colonel Antonio de la Cruz Estigarribia crossed the Argentine border south of Encarnación in May 1865, driving for Rio Grande do Sul.

For all practical purposes, this battle decided the outcome of the war in favor of the Triple Alliance; from that point onward, it controlled the waters of the Río de la Plata basin up to the entrance to Paraguay.

[42] The baron of Porto Alegre set out for Uruguaiana, a small town in the province's west, where the Paraguayan army was besieged by a combined force of Brazilian, Argentine and Uruguayan units.

[55] On 12 September 1866, after the defeat in the Battle of Curuzú, Solano López invited Mitre and Flores to a conference in Yataytí Corá, which resulted in a "heated argument" among both leaders.

He further criticized Porto Alegre: "It is impossible to imagine a greater military nullity than this general, to which it can be added Tamandaré's dominating bad influence over him and the negative spirit of both in relation to the allies, owning to passions and petty interests.

[16]: 73 The Paraguayans, commanded by general Bernardino Caballero breached the Argentine lines, causing enormous damage to the Allied camp and successfully capturing weapons and supplies, very needed by López for the war effort.

The fighting continued until dawn when the warships Brasil, Herval, Mariz e Barros and Silvado approached and shot the Paraguayans, who gave up the attack, losing 400 men and 14 canoes.

This was followed by negotiations between the Allied countries, which put aside some of the more controversial points of the Treaty of the Triple Alliance; on 11 June, agreement was reached with Paraguayan opposition figures that a three-man Provisional government would be established.

[citation needed] Later Bedoya made a trip to Buenos Aires and absconded with church silver from Paraguay (which had been given to him to serve as guarantee for a loan), and then disappeared from public life.

The remaining member, Cirilo Rivarola, was then immediately relieved of his duties by the National Assembly, which established a provisional Presidency, to which it elected Facundo Machaín, who assumed his post that same day.

[89] After a successful beginning which included victories over the remnants of Solano López's army, the Count fell into depression and Paranhos became the unacknowledged, de facto commander-in-chief.

At the beginning of the conflict, most Brazilian soldiers came from the north and northeast regions;[citation needed] the change from a hot to a colder climate, combined with restricted food rations, may have weakened their resistance.

First, to defend itself against Indian incursions, both in colonial times and after, the authorities in Asunción had established some border forts on the west bank of the river Paraguay—a coastal strip within the Chaco.

The second exception was that in 1854, the government of Carlos Antonio López established a colony of French immigrants on the right bank of the River Paraguay at Nueva Burdeos; when it failed, it was renamed Villa Occidental.

Paraguay is estimated to have lost up to 69% of its population, most of them due to illness, hunger and physical exhaustion, of which 90% were male according to the most extreme reports, and also maintained a high debt of war with the allied countries that, not completely paid, ended up being pardoned in 1943 by the Brazilian President Getúlio Vargas.

[136] A popular belief among Paraguayans and Argentine revisionists since the 1960s contends that the outbreak of war was due to the machinations of the British government, a theory which historians have noted has little to no basis in historical evidence.

They have also noted that in 1864, a British diplomat wrote a letter to Solano López asking him to avoid initiating hostilities in the region, and there remains no evidence that Britain "forced" the allies to attack Paraguay.

Tate noted that: Whatever his dislike of Paraguay, Thornton appears to have had no wish that its quarrels with Argentina and Brazil, rapidly worsening at the time of his visit to Asunción, should develop into war.

In addition, they also noted that the war damaged international commerce (including Britain's), and the British government disapproved of the secret clauses in the Treaty of the Triple Alliance.

[151][152] William Doria (the British Chargé d'Affaires in Paraguay who briefly acted in Thornton's place), joined French and Italian diplomats in condemning Argentina's President Bartolomé Mitre's involvement in Uruguay.