The Platine War was fought between the Argentine Confederation and an alliance consisting of the Empire of Brazil, Uruguay, and the Argentine provinces of Entre Ríos and Corrientes, with the participation of the Republic of Paraguay as Brazil's co-belligerent and ally. The war was part of a decades-long dispute between Argentina and Brazil for influence over Uruguay and Paraguay, and hegemony over the Platine region. The conflict took place in Uruguay and northeastern Argentina, and on the Río de la Plata. Uruguay's internal troubles, including the longrunning Uruguayan Civil War, were heavily influential factors leading to the Platine War.

The Empire of Brazil was a 19th-century state that broadly comprised the territories which form modern Brazil and Uruguay until the latter achieved independence in 1828. Its government was a representative parliamentary constitutional monarchy under the rule of Emperors Pedro I and his son Pedro II. A colony of the Kingdom of Portugal, Brazil became the seat of the Portuguese Empire in 1808, when the Portuguese Prince regent, later King Dom John VI, fled from Napoleon's invasion of Portugal and established himself and his government in the Brazilian city of Rio de Janeiro. John VI later returned to Portugal, leaving his eldest son and heir-apparent, Pedro, to rule the Kingdom of Brazil as regent. On 7 September 1822, Pedro declared the independence of Brazil and, after waging a successful war against his father's kingdom, was acclaimed on 12 October as Pedro I, the first Emperor of Brazil. The new country was huge, sparsely populated, and ethnically diverse.