Argentine War of Independence Chile, allied with the Mapuches. On April 4, Argentine Colonel Juan Gregorio de Las Heras had occupied Concepción, but the Royalists retreated to Talcahuano. In early 1818, Royalist reinforcements from the Viceroyalty of Peru arrived, commanded by general Mariano Osorio, and advanced towards the capital. San Martín then turned to scorched earth tactics and ordered the evacuation of Concepción, which he thought was impossible to defend. On 18 February 1818, the first anniversary of the battle of Chacabuco, Chile declared its independence from the Spanish Crown. On March 18, 1818, Osorio led a surprise attack on the joint Argentine-Chilean army,
José de San Martín Nearly 700 expeditionary soldiers of New Granada deserted and joined the patriots. Several populations in the north of Peru supported San Martín, and Arenales defeated the royalists at the Battle of Pasco. More than 300 royalists joined the patriots, including Andrés de Santa Cruz. However, the plans did not fully work as intended. The native populations that joined Arenales could not resist the royalist counter-attacks, and the slaves did not join the army in the expected numbers. The Argentine provinces could not send the supporting army that San Martín had requested earlier, and the Army of the North no longer