Uruguayan War: Brazilian and Colorado Party forces captured the city of Paysandú from its Uruguayan defenders.

The Uruguayan War was fought between Uruguay's governing Blanco Party and an alliance consisting of the Empire of Brazil and the Uruguayan Colorado Party, covertly supported by Argentina. Since its independence, Uruguay had been ravaged by intermittent struggles between the Colorado and Blanco factions, each attempting to seize and maintain power in turn. The Colorado leader Venancio Flores launched the Liberating Crusade in 1863, an insurrection aimed at toppling Bernardo Berro, who presided over a Colorado–Blanco coalition (fusionist) government. Flores was aided by Argentina, whose president Bartolomé Mitre provided him with supplies, Argentine volunteers and river transport for troops.

The Colorado Party is a major political party in Uruguay. Founded in 1836 by General Fructuoso Rivera, the first president of Uruguay, it is one of the country's oldest active political parties along with the National Party, their origin dates back to the establishment of Uruguay as an independent state.

The siege of Paysandú began on 3 December 1864, during the Uruguayan War, when Brazilian forces and Colorado forces attempted to capture the city of Paysandú in Uruguay from its Uruguayan Army defenders. The siege ended on 2 January 1865, when the Brazilian and Colorado forces conquered the town.

Paysandú is the capital and most populous city of the Paysandú Department in western Uruguay. Located on the banks of the Uruguay River, it is the country's fourth-largest city and a vital cultural and economic hub, with agriculture, tourism, and manufacturing serving as key industries.