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 Goyeneche and Joaquín de la Pezuela, an able and experienced soldier, had the advantage, he negotiated with Goyeneche a 40-day armistice. The Assembly in Buenos Aires and the viceroy of Peru, José Fernando de Abascal, disapproved of this agreement. The royalists attacked by surprise, disregarding the agreement, before the arrival of reinforcements at the Battle of Vilcapugio on 1 October 1813. The royalist army, commanded by brigadier Joaquín de la Pezuela and with 4,000 men and 12 pieces of artillery confronted a patriot army with a high morale composed of 3,500 men, 14 pieces of artillery and cavalry mounted mostly