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 bulk of the royalist forces, while the center was hit by the soldiers of Pio Tristan. Many patriotic soldiers recruited at the Upper Peru surrendered or fled, and many of the recruits in La Paz switched sides during the battle. The Saavedrist Juan José Viamonte was instrumental in the defeat, by refusing to join the conflict. Although the casualties of the Army of the North were not substantial, it was left desmoralized and disbanded. The inhabitants of Upper Peru left them and welcomed the royalists back, so the army had to quickly leave those provinces. However, the resistance of Cochabamba