In exile in Argentina, O'Higgins joined forces with José de San Martín. Their combined army freed Chile with a daring assault over the Andes in 1817, defeating the Spaniards at the Battle of Chacabuco on February 12 and marking the beginning of the "Patria Nueva". San Martín considered the liberation of Chile a strategic stepping-stone to the emancipation of Peru, which he saw as the key to hemispheric victory over the Spanish.