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,[35][36] 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.[37] Brazil's Conservative Cabinet decided to form military alliances with the countries threatened by the dictator.[38] On 4 September 1851, Brazil's army, commanded by Luis Alves de Lima e Silva (then Count of Caxias), crossed the border into Uruguay.[39]