Thirty-Three Orientals in the context of Juan Antonio Lavalleja

The Cisplatine War was an armed conflict fought in the 1820s between the Empire of Brazil and the United Provinces of the Río de la Plata over control of the Banda Oriental following its annexation by Brazil as the Cisplatina province. It was fought in the aftermath of the United Provinces' and Brazil's independence from Spain and Portugal, respectively, and resulted in the independence of Cisplatina as the Oriental Republic of Uruguay.

In 1816, the United Kingdom of Portugal, Brazil and the Algarves carried out an invasion of the Banda Oriental and, after defeating the local resistance led by José Gervasio Artigas, annexed it under the name of Cisplatina. After Brazil's independence in 1822, Cisplatina remained as part of Brazil. Wishing to gain control of the region, the United Provinces sent a diplomatic mission to Brazil in 1823 to negotiate a peaceful Brazilian withdrawal, but it failed. In 1825, a group of patriots known as the Thirty-Three Orientals, supported by the Argentine government and led by Juan Antonio Lavalleja, launched a rebellion against Brazil. On 25 August of that year, in the Congress of Florida, they declared Cisplatina's independence from Brazil and its unification with the United Provinces. After a series of initial skirmishes, they defeated the Brazilians at the battles of Rincón and Sarandí, prompting the Argentine Congress to proclaim Cisplatina reintegrated into the United Provinces on 25 October. In response, Brazil declared war on the United Provinces on 10 December 1825 and imposed a naval blockade on the River Plate.