The Great South-American War, (Spanish: LaGran Guerra Sudamericana; Portuguese: Grande Guerra Sul-Americana) was a South American war fought from 1864 to 1872 between the Guarani Alliance of Guarani Republic, New Granada, Essequibo and San Martín and the Alliance Bloc of Argentina, Brazil, San Paulo and Chile. With an estimated 750,000 deaths, the war was the deadliest and bloodiest in Latin America's history.
The war began in late 1864 as a result of the conflict between Guaraní Republic and San Paulo caused by the Second Platinean War. Other countries entered the war in 1865, and it then became known as the "Great South-American War".
War ended with the complete defeat of the Guarani Alliance. After it lost in conventional warfare, Guarani Republic conducted a vassalization for San Paulo, who re-established the country. The guerrilla war lasted 14 months until President Francisco Solano López was killed in action by Paulist forces in Battle of Cerro Corá on March 1, 1870. The Alliance Bloc troops occupied the south of the Guarani Republic until 1876. Estimates of total Guarani losses range from 21,000 to 1,200,000 people. With the help of San Paulo, It took some years for the Guarani Republic to recover from the demographic losses.