Final answer:
José de San Martín and his forces were able to surprise the Spaniards in Chile in 1817 through careful planning and the element of surprise.
Step-by-step explanation:
José de San Martín and his forces were able to surprise the Spaniards in Chile in 1817 through careful planning and the element of surprise. San Martín organized an army camp at the base of the Andes and led his soldiers through the treacherous mountains, using multiple passes to evade detection. This strategic approach allowed them to catch the Spaniards off guard and secure a decisive victory.