In 1864, Brazil intervened in Uruguay’s civil conflict, citing attacks and losses suffered by Brazilian residents near the border. Paraguay’s president Francisco Solano López warned that a Brazilian occupation of Uruguay would threaten the regional balance of power, setting the stage for war.
Paraguayan forces seized the Brazilian steamer Marquês de Olinda on the Paraguay River, escalating the dispute with Brazil from diplomacy toward open conflict. The capture helped trigger rapid military planning and mobilization on both sides.
Paraguay launched an offensive into Brazil’s remote Mato Grosso region, aiming to disrupt Brazilian power and secure leverage early in the conflict. This opened the war’s first major land campaign, stretching Brazil’s defenses across vast distances.
Brazil, Argentina, and Uruguay signed the Treaty of the Triple Alliance in Buenos Aires, formally coordinating their war aims and military cooperation against Paraguay. The treaty turned the conflict into a large multinational war and shaped how peace terms would later be negotiated.
Brazil defeated Paraguay’s fleet on the Paraná River, preventing Paraguay from controlling key waterways. This battle mattered because rivers were the main supply routes in the region, and the result gave the Allies a stronger position for future offensives.
A Paraguayan force operating in southern Brazil became trapped and, after weeks of siege, surrendered due to hunger and disease. The surrender ended a major Paraguayan incursion into Brazilian territory and reduced Paraguay’s ability to pressure Brazil away from the main front.
Paraguay attacked the Allied camp at Tuyutí in one of the war’s largest battles. The Allies held their positions, and Paraguay suffered extremely heavy losses, weakening its ability to launch large offensives afterward.
The Allies attacked Paraguayan fortifications at Curupayty and were repulsed with severe casualties. The defeat slowed the Allied advance and contributed to a long period of operational delay, giving Paraguay time to hold key defensive positions longer.
Brazilian forces recaptured Corumbá after roughly two years of Paraguayan control. The victory strengthened Brazil’s position in its interior frontier and signaled that Paraguay’s early gains in Mato Grosso could be rolled back over time.
Brazilian armored vessels ran past the powerful fortress of Humaitá on the Paraguay River, a key defensive barrier protecting the approach to Paraguay’s heartland. This action mattered because it reduced the fortress’s control of river traffic and helped the Allies tighten the strategic noose around Paraguay.
Allied forces entered and occupied Paraguay’s capital, Asunción, after Paraguayan authorities evacuated the city. The occupation shifted the war into a pursuit phase, as Solano López continued resistance from the interior while Paraguay’s government and economy were disrupted.
Brazilian troops caught López’s remaining forces at Cerro Corá, where López was killed. His death ended organized Paraguayan resistance and is widely treated as the war’s endpoint, though occupation and boundary settlements continued afterward.
Paraguay and Brazil signed a separate peace and boundary treaty in Asunción. The agreement formalized Brazil’s postwar border gains and marked a shift from wartime operations to long-term settlement, even as other territorial questions in the region remained contested.
Paraguay and Argentina concluded a postwar border treaty that settled most Argentine territorial claims and helped bring the Allied occupation to a close. The treaty contributed to a new regional map and closed a major diplomatic chapter of the war’s aftermath.
Paraguayan War (Triple Alliance War) (1864–1870)