Brazil had carried out three political and military interventions in the politically unstable Uruguay: in 1851 against Manuel Oribe in order to fight Argentine influence in the country and to end the Great Siege of Montevideo; in 1855, at the request of the Uruguayan government and Venancio Flores, leader of the Colorado Party, which was traditionally supported by the Brazilian empire; and in 1864, against Atanasio Aguirre.