In New Spain, royalists, after defeating the insurgents, proclaimed a negotiated separation from Liberal Spain through the Plan of Iguala, which they negotiated with the remaining patriots, and the Treaty of Córdoba, which they negotiated with the new head of government, Juan O'Donojú. In Peru Viceroy Joaquín de la Pezuela was discredited after a royalist expedition to Chile under Mariano Osorio was defeated and advances in Peru were made by José de San Martín. The viceroy was overthrown on 29 January 1821, in Asnapukyu "(Aznapuquio)", in a coup by General José de la Serna, who proclaimed his adhesion to the restored Spanish Constitution.