In the middle of the 19th century, vast tracts of South America were undeveloped, railways were few and short,[5] and surfaced roads practically did not exist;[6] so navigable rivers were "vital arteries".

However, as noted by John Hoyt Williams, "the dizzying speed with which his nation was 'modernized' and strengthened tempted López to flex his new muscle and seek an ever-expanding, activist role in international affairs".

[37] In 1862, the Uruguayan Blanco Party, traditionally hostile to Brazil, and now alarmed because its bitter enemies[38] had seized power in Buenos Aires too, [39] felt itself to be acutely short of allies.

[41] This campaign, which continued through 1864, insinuated that Buenos Aires had designs on both Paraguay and Uruguay, who should make a warlike alliance, detach the Argentine provinces of Corrientes and Entre Ríos and seize Martín García Island.

Paraguay, difficult of access, might have resisted Brazilian retaliation for a long time, but now it took a step that was to give Brazil what it had lacked hitherto: a good forward base from which to attack it.

In March 1865, a change of government in Brazil had Liberal Party member Francisco Otaviano de Almeida Rosa sent on a special mission to the River Plate region.

[65] The Paraguayan attack on Argentine territory (13 April) precipitated the Brazil-Argentina alliance so that the 40-year old Otaviano had to negotiate its terms on the spot, without specific instructions from Rio de Janeiro since there was no telegraph link with that capital.

[66] Otaviano thought the Argentine government meant to get aid from Brazil without assuming any obligations so that once the conflict was over, it could reincorporate Paraguayan territory into an Argentine-led successor to the old Viceroyalty of the River Plate.

When the Brazilian government discovered what Otaviano had negotiated, particularly his concessions toward Argentina, it was not pleased, and the terms of the treaty were strongly criticised by the Conservative opposition.

After the War of the Triple Alliance, by a long-drawn out process, Brazil managed to prevent Argentina from getting territory to the north of the Pilcomayo, and that river is still the international boundary between the Argentine province of Formosa and the Paraguayan department of Presidente Hayes.

2The pay, victuals, munitions of war, arms, clothing, equipment, and means of transport of the allied troops will be for the account of the respective States.

The allies pledge themselves solemnly not to lay down their arms unless by common accord, nor until they have overthrown the present Government of Paraguay, nor to treat with the enemy separately, nor sign any Treaty of peace, truce, armistice, or Convention whatsoever for putting an end or suspending the war, unless by a perfect agreement of all.

The independence, sovereignty, and territorial integrity of the Republic of Paraguay will be guaranteed collectively in conformity with the foregoing Article by the High Contracting Parties during the period of five years.

The allies will appoint in due season the Plenipotentiaries required to celebrate the arrangements, Conventions or Treaties that may have to be made with the Government that shall be established in Paraguay.

[90] However, in a note published in the Portuguese translation of Schneider's work (1902), the Brazilian diplomat José Maria da Silva Paranhos qualified that assertion as follows:[91] There only was not approved by the Argentine Congress the clause relating to the fortifications, and this lack of approbation, kept secret, was only communicated to Brazil long after the war.

[94] Argentina's refusal to ratify the Protocol came to light when it and Brazil were disputing the meaning and effect of the treaty, and the Brazilian government published some of the correspondence.

It was never determined whether the Argentine legislature's refusal to ratify Article 1 of the Protocol was effective according to the law of nations or whether it was ineffective because it was not communicated to Brazil in a timely manner.

Because Brazil had incomparably the biggest navy, however, they agreed that command of the naval forces should be conferred initially on the Brazilian admiral Joaquim Marques Lisboa, the Viscount of Tamandaré.

As against that, however, Domingo Faustino Sarmiento, winner of the 1868 presidential election on an anti-war platform, did try to bring about Argentina's unilateral withdrawal — Article VI or not.

Note that, by the second indent of this Article, Argentina was supposed to receive territory on the right bank of the River Paraguay (i.e. in the Gran Chaco) all the way up to Bahia Negra.

For the reasons explained in the second section of this Article, from the moment the Treaty was signed Brazil set out to frustrate Argentina's claim to this territory, and succeeded.

[108] The British consul at Rosario, Thomas Hutchinson, thought that the "principal object" referred to the demolition of the Fortress of Humaitá, though not mentioned until the Protocol.

[109] Article 1 expressly provided that the Fortress of Humaitá must be demolished and that "it shall not be permitted that others of an equal nature should be erected, which might impede the faithful execution of the Treaty."

That said, some provisions of the Treaty were obvious at the time or easy to guess (such as that there was some sort of alliance against López) and others were less so (such as the precise extent to which Argentina's territorial claims were to be vindicated).

The British chargé d'affaires in Montevideo, William Garrow Lettsom, had asked Uruguayan Foreign Minister Carlos de Castro directly whether the allies planned to partition Paraguay "like some South American Poland".

On the other hand, when the treaty was published in a Paraguayan weekly, many people were convinced that López was right to wage war with the Allies and that "Paraguay was compelled to fight for her very existence.

[120] For a time Brazilian forces continued to occupy the Isla del Cerrito, an island near the mouth of the Paraguay River that was claimed by Argentina but which had served as Brazil's main naval base during the war.

The American minister in Rio de Janeiro also thought that Argentina was behind an unsuccessful attempt to topple president Salvador Jovellanos of Paraguay, who, the Argentines said, was a Brazilian puppet.

[127] In 1875, Argentina started fortifying Martín García Island again, which the U.S. saw as a full treaty violation, threatening free navigation: "The problem was compounded by the appearance of two new Argentine ironclads, which caused further Brazilian apprehension and curiosity".

It appeared that Tejedor had been negotiating Argentina's own unilateral treaty with Paraguay, taking advantage of the fact that Paraguayan envoy Jaime Sosa was in Rio de Janeiro at the time.