An Army Crosses the Andes to Challenge Spanish Rule

In January 1817, General José de San Martín launched an ambitious military expedition from the Argentine city of Mendoza, leading a combined force of Argentine troops and exiled Chilean patriots into the high passes of the Andes. The strategic goal was to liberate Chile from royalist control and establish a base from which to threaten the royalist stronghold in Lima, Peru. Earlier attempts to strike royalist power directly through Upper Peru had encountered immense logistical obstacles, prompting San Martín to reconsider his route. A route through Chile and then by sea toward Peru offered a different way to reach the center of royalist power. Historians have compared this approach with earlier proposals, but a direct chain of borrowing is not securely established.

The geopolitical situation in Chile had shifted dramatically after local patriots removed their governor in 1810 and established an autonomous junta, initiating the era known as the Patria Vieja. Royalist forces reasserted control following their decisive victory at the Battle of Rancagua in 1814. In the aftermath of this defeat, prominent Chilean leaders, including Bernardo O'Higgins, fled across the mountains into the Province of Cuyo. San Martín welcomed these political refugees in Mendoza, where O'Higgins and other Chilean exiles integrated into the planning and leadership of what became the Army of the Andes.