In July 1836, Fructuoso Rivera, offended by the results of an examination of his administration and also dismissed from the post of commander of the army, rebelled against the government of Manuel Oribe.

Under pressure from the situation at the Río de la Plata and besieged at Montevideo, Oribe announced his resignation on 24 October 1838, allowing Rivera to assume power.

The Federalist governor of Buenos Aires Province, Juan Manuel de Rosas, refused to recognize Rivera's government as legitimate and allied himself with Oribe.

After the victory at the Battle of Arroyo Grande, Oribe's army crossed the Uruguay River and began the siege of Montevideo on 16 February 1843.

While Oribe besieged Montevideo, the Colorados organized a defense force under the command of José María Paz and Melchor Pacheco.

He was joined by several groups from the French, Spanish and Italian communities, all of them immigrants and mostly residents of Montevideo who formed "legions" that numerically exceeded the Oriental troops that the Colorados had.

Uruguayan diplomat Andrés Lamas gained the Empire of Brazil's support and commitment to intervene in the siege of the side of the Defense Government.

After rejecting an offer to join on the side of the Defense Government, Ignacio Oribe attempted to engage the invaders, resulting in a mass desertion of his troops.

On 4 September, 16,000 Brazilian troops led by Luís Alves de Lima e Silva, Count of Caxias entered Uruguay.

[20] In addition, Brazil, Uruguay, and Entre Rios formed an alliance to invade Argentina with the goal of deposing Juan Manuel de Rosas.