Viceroyalty of Peru arrived in Lima with Antonio José de Sucre to plan the offensive. In February 1824 the royalists briefly regained control of Lima. Olañeta's Rebellion started by surprise and the entire royalist army of Upper Peru (today's Bolivia) revolted, led by Pedro Antonio Olañeta (royalist) against La Serna, the viceroy of Peru (a liberal). This broke the royal army and started a civil war in Upper Peru. Having regrouped in Trujillo, Bolívar in June led his rebel forces south to confront the Spanish under Field Marshal José de Canterac. The two armies met on the plains of Junín on August 6,
First Upper Peru campaign authorities. The May Revolution, in Buenos Aires, was more successful, and ousted the viceroy Baltasar Hidalgo de Cisneros. The Primera Junta, which replaced him, prepared a military expedition to Upper Peru to secure the control of the area, while another expedition headed to Paraguay. Before proceeding to Upper Peru, this military campaign defeated a counter revolution in Córdoba, organized by the former viceroy Santiago de Liniers. Ortiz de Ocampo disobeyed orders to execute the prisoners, sending them to Buenos Aires instead. As a result, the Junta appointed Juan José Castelli as commander of the Army of the North instead of