United Provinces of South America in the context of Congress of Tucumán

The Independence of the Argentine Republic (or La Independencia de Argentina in Spanish) was declared on July 9, 1816, by the Congress of Tucumán. In reality, the congressmen who were assembled in Tucumán declared the independence of the United Provinces of South America, which is one of the official names of the Argentine Republic. The Federal League Provinces, at war with the United Provinces, were not allowed into the Congress. At the same time, several provinces from the Upper Peru that would later become part of present-day Bolivia, were represented at the Congress.

The Army of the Andes (Spanish: Ejército de los Andes) was a military force created by the United Provinces of the Río de la Plata (Argentina) and assembled by General José de San Martín as part of his campaign to liberate Chile from the Spanish Empire. In 1817, it crossed the Andes Mountains from the Argentine province of Cuyo (with its staging point being the present-day province of Mendoza, Argentina) and succeeded in its objective by driving the Spanish out of Chile.

The exact number of soldiers in the army varies among sources, with estimates ranging from as low as 3,500 to as high as 6,000 men. The army was composed of Argentines and Chileans, and included approximately 1,200 auxiliaries who assisted with provisioning and supply, along with 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 in preparation for their mission. Although the army was less experienced, San Martín aimed to lead a properly disciplined and equipped force into battle, not a mere "motley crew."