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 a victory at Utarango but was later defeated on 12 February by the San Juan river. Rondeau received an order to retreat to Tucumán. The army, almost beaten, marched for nine months going through Potosí and Humahuaca until reaching Tucumán. On 7 August 1816 at Trancas, Rondeau was replaced again by Manuel Belgrano. Martín Miguel de Güemes was named commander of the northern border. Belgrano moved the army to the citadel built by San Martín in the city of Tucumán. There he attempted to rebuild the morale, and materials, in search for a new action in Upper Peru, combining with