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,
Army of the North of the Royalist forces in Upper Peru. On 12 May Orozco commanding a force of 4,000 men advanced to Jujuy, and on 28 May occupied the city, then on 31 May occupied Salta. On 2 June the royalist forces defeated the patriots at Chamical (southwest of the city of Salta). At the battle of Las Cañas lieutenant colonel Rojas was killed but the force of 400 royalists was defeated. On 8 June there was a new independentist victory at Cuesta de la Pedrera (southeast of Salta), dispersing 2,000 royalists who retreated to Jujuy. At the battle of Yala another royalist