Don Juan Manuel de Rosas, the dictator of Argentina, had assisted the separatist rebels in the Brazilian province of Rio Grande do Sul during the 1830s, and continued to attempt its annexation. In addition to the threat to Brazil's territorial integrity, Rosas had ambitions to conquer Paraguay, Uruguay and Bolivia. Brazil's Conservative Cabinet decided to form military alliances with the countries threatened by the dictator. On 4 September 1851, Brazil's army, commanded by Luis Alves de Lima e Silva (then Count of Caxias), crossed the border into Uruguay.