Army of the Andes The Army of the Andes ( ) was a military force created by the United Provinces of the Río de la Plata ( Argentina ) and mustered by general José de San Martín in his campaign to free Chile from the Spanish Empire . In 1817 , it crossed the Andes Mountains from the Argentinian province of Cuyo ( his staging point being the current - day province of Mendoza , Argentina ) , and succeeded in its objective by dislodging the Spanish from the country . The exact number of the army varies between different sources ; some have put the number as low as 3500 , while others have it being as high as 6000 men . The army consisted of Argentinians and Chileans , and included some 1200 auxiliaries to help in provisioning and supply , as well as a complement of artillery . The Congress of Tucumán endorsed San Martín ' s proposal to form an army to fight the royalists in Chile , and between August 1814 and February 1817 , San Martín trained his troops to prepare them for their ordeal . While the army was made up of a less than experienced military force , San Martín intended to lead , with regular discipline and equipment , a proper army and not a " motley crew " into battle . For the crossing of the mountains , the Army was divided into two main columns , the first , commanded by Captain General San Martín and supported by Brigadier Major Miguel Estanislao Soler and Brigadier Bernardo O ' Higgins , would take the Los Patos Pass and the second , commanded by Colonel Juan Gregorio de las Heras , would take the Uspallata Pass , which at its highest reaches some twelve thousand feet above sea level . Because this second pass was more negotiable , the artillery was taken in the second column . These two divisions were the main body of the Army , but there were smaller detachments sent to the north and south as flanking wings . The smaller division to the north was composed of some 130 infantry as well as a group of Chilean expatriate s , and was under the command of Juan Manuel Cabot . To the south was a group under the command of the Chilean Ramón Freire Serrano . After their 25 - day journey across the Andes , the Army of the Andes successfully met royalist forces in the Battle of Chacabuco . After the victory , they entered Santiago de Chile , where San Martin was unanimously elected Supreme Director but by his own resolve , as well as from instructions received from Buenos Aires , the general declined . After his refusal , O ' Higgins was finally elected . Under Argentinian officers , the Chilean army resurrected and San Martín was designated commander of the " United Army " , which was an army that combined the forces of the Army of the Andes and Chilean troops . This new army fought the counterattack of royalist Army of Osorio at battles of Cancha Rayada and Maipú . Composition of the Army of the Andes . Black soldiers . The number of black soldiers in the army of San Martin was numerous and grouped to form the majority of the regiments of soldiers called numbers 7 , 8 and 11 infantry Andes . According to military doctrine of St . Martin , colored soldiers would serve better in the infantry branch among the three arms of the army of the Andes , in fact blacks representing 2 / 3 of soldiers of the army of the Andes , estimated between 2 , 000 and 3 , 000 Argentine freedmen who crossed the Andes to Chile in 1817 with San Martin . Black troops were mainly recruit of slaves which Lynch estimates a figure of 1 , 554 slaves . Most recruit in the provinces . Of those 2 , 500 black soldiers who began the crossing of the Andes , only 143 survived to be repatriated . In all of these black regiments commissioned officers should be white under Argentine law . But San Martin sought to change the rules so that at least the black soldiers reached grades corporals and sergeants . But traditionally the Spanish colonial army battalions organized divided into castes of black slaves and free blacks , and San Martin believed even harder to gather people of color and whites fighting as soldiers in the same unit . later both regiments 7 and 8 will be unified in Peru in the black regiment of the Río de la Plata . Units 1814 - 1815 . " Argentine Units " " Chilean Units " " Combined Argentine - Chilean units "