Alvear returned to Argentina in 1822 thanks to an amnesty law ("Ley del olvido"). At the end of 1823, Bernardino Rivadavia named him minister plenipotentiary to the United States. Before going to Washington, Alvear stopped in London and managed to get an interview with George Canning, the British Foreign Secretary. Weeks after this interview, the British government formally recognized the independence of the United Provinces of the Rio de la Plata. In 1825 Alvear was sent by the Buenos Aires government to Bolivia to meet with Simón Bolivar. The real objective of this mission was to seek Bolivar's support in the looming war with the Empire of Brazil, over the Banda Oriental. Alvear had also a project of his own: the creation of big republic in South America comprising Argentina, Chile, Bolivia, Paraguay and Uruguay. He asked Bolivar to be its first president. The Venezuelan leader was sympathetic to this project but dissensions in Gran Colombia forced him to abandon it.