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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 Brazil's 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. The United Provinces managed to occupy the Uruguayan countryside with the help of the local insurgents, however, its forces never managed to capture Montevideo and Colonia del Sacramento or penetrate deeply into Brazilian territory. Likewise, the Brazilians did not manage to regain control of the countryside or achieve a decisive victory in order to repel the Argentines, being defeated at the battle of Ituzaingó. Thus, the war on land reached an impasse. At sea, however, the Brazilian Navy obtained better results, despite the Argentine resistance, whose small fleet, led by Irish-born admiral William Brown, was mostly destroyed. The economic burden and internal political disputes caused by the war in both states, especially the Brazilian naval blockade and the impasse on land, led both countries to start peace negotiations. In 1827, the Argentine minister plenipotentiary Manuel José García signed a peace treaty with Brazilian representatives, recognizing Brazil's sovereignty over Cisplatina and agreeing to pay Brazil a war indemnity. The treaty was rejected by Argentine president Bernardino Rivadavia, but its terms generated enormous backlash forcing the president to present his resignation. Manuel Dorrego was then elected to succeed him and continue the war. The conflict continued until 27 August 1828, when Argentine and Brazilian representatives, under British mediation, signed the Preliminary Peace Convention of 1828, by which Cisplatina would become an independent state and hostilities would cease. After the war, tensions in Argentina between the Federalists and the Unitarians increased. Manuel Dorrego, a Federalist, was deposed and executed by Juan Lavalle and the country fell into a civil war. In Brazil, the war's financial cost, aggravated by the damage done to Brazilian trade by Argentine corsairs, and the loss of Cisplatina, added to the internal political disputes surrounding emperor Pedro I, which ultimately led him to abdicate the throne in favour of his 5-year-old son Pedro II in 1831, ushering the regency period.