In the early hours of February 12, 1817, Argentine revolutionary José de San Martín leads his troops down the slopes of the Andes Mountains towards the Spanish forces defending Chile. By nightfall, the Spanish would be routed, the fledgling nation of Chile would have taken a major step toward independence.
San Martín was already a celebrated figure across South America, having liberated Argentina from Spanish rule. As his armies moved through the southern part of the continent, Simón Bolívar waged a similar campaign of liberation in the north, and by 1817 much of the continent was either independent or in a state of revolt. Though uprisings and guerrilla attacks had occurred throughout the narrow region between the Andes and the Pacific Ocean, Chile and its ports remained under Spanish control.
San Martín led his army, the Army of the Andes, on an arduous march into Chile. It is estimated that as much as one third of his 6,000 men died in the crossing, and over half his horses were lost. Nonetheless, the patriots outnumbered the Spanish in the region when they finally reached the other side. Knowing Spanish reinforcements were nearby, San Martín pressed the advantage, ordering an early-morning advance down the slopes on February 12th. Two halves of his force were to convene on the Spanish at once, but one of his officers, a Chilean (of partially Irish descent) named Bernardo O'Higgins, could not wait. O'Higgins' contingent raced down the mountains, giving the Spanish a numerical advantage and forcing San Martín into a somewhat haphazard assault. Nonetheless, by afternoon the patriots had forced the Spanish back into defensive positions around a local ranch, the Rancho Chacabuco. As O'Higgins made another charge, General Miguel Estanislao Soler moved his men to the other side of the ranch, cutting off the Spanish retreat. The result was disaster for the Spanish, who suffered 500 casualties and lost even more prisoners of war. Meanwhile, only a dozen patriot soldiers were reported dead, although roughly 120 would eventually die from wounds suffered in the battle.
The quick and total victory cleared the path to Santiago, the capital of Chile. Though it would take over a year for final victory to be assured, Chacabuco was seen as the pivotal moment in Chilean independence—formal independence was declared on February 12th, 1818, the first anniversary of the battle. The Battle of Chacabuco marked a crucial moment not only in Chilean history but also in the history of the continent and in the lives of San Martín, who added the liberation of Chile to his long list of achievements, and of O'Higgins, who would soon become Supreme Dictator of his newly-independent nation.