(hwän mänwĕl' dā rô'säs), 1793–1877, Argentine dictator, governor of Buenos Aires prov. (1829–32, 1835–52). As a boy he served under Jacques de Liniers against the British invaders of the Rio de la Plata (1806–7). Most of his youth was spent in the cattle country, where he built his fortune through large-scale ranching. As a full-fledged caudillo, he began his political career in 1820 by leading a force of gauchos in support of the conservatives and federalism. After the deposition and execution (1828) of Manuel Dorrego, he became the federalist leader. His rise to power represented the rise of the estancieros, the new landed oligarchy based on commercial ranching. Together with Estanislao López, he defeated Juan Lavalle, and became governor (1829) of Buenos Aires with dictatorial powers. Aided by López and Juan Facundo Quiroga, he waged a sanguinary campaign against the unitarians, destroying their movement, at least temporarily. He surrendered office in 1832, and went on to wage a successful expedition against the indigenous peoples. In 1835, Rosas again became governor; by machinations and arrangements with other provincial chiefs, he assumed the dictatorship of most of Argentina. Rosas's politics were, in practice, antifederalist despite his formal allegiance. He came to represent the hegemony of Buenos Aires. His government became a ruthless tyranny. Assisted by spies, propagandists, and the Mazorca (a secret political society that degenerated into a band of assassins), he instituted a regime of terror. Though he was adulated in public, successive and continuous revolutions were organized against his rule. Secret revolutionary groups—notably the Asociación de Mayo, founded by Esteban Echeverría—were formed. Ironically, by driving into exile many of the fine minds in Argentina—Juan Bautista Alberdi, Bartolomé Mitre, and especially Domingo F. Sarmiento—he contributed unwittingly to the creation of several classics of South American literature and social analysis. Rosas became involved in a dispute with the United States and Britain over the Falkland Islands. His ambition led him to interfere in Uruguay, where he supported Manuel Oribe. His suspected designs to reduce Paraguay and Uruguay to dependent Argentine states led to two blockades by France and Great Britain (1838–40, 1845–50), greatly hurting Argentine commerce. Resentment against the dominance of Buenos Aires resulted in a final, successful revolution against Rosas. Aided by Brazil and Uruguay, Justo José de Urquiza crushed the tyrant's army at Monte Caseros (1852), and the dictator fled to England, where he lived in exile until his death. Rosas contributed greatly to the unification of Argentina.
- See study by J. Lynch (1981).