Rio Branco's work in the press, highlighting threats posed by the armed conflicts in the Platine republics (Argentina and Uruguay), attracted the attention of Honório Hermeto Carneiro Leão, Marquis of Paraná, who invited him to act as secretary on a diplomatic mission to Montevideo. They were successful in forging alliances, which contributed to the eventual fall in 1852 of Juan Manuel de Rosas, an Argentine dictator who had declared war on Brazil. In 1853 Rio Branco joined the Marquis of Paraná's Conservative Party as well as the cabinet over which the latter presided.