The Spanish indeed had great success in conquering the Naive Americans in the Americas. I feel there are many, not just one answer to why this was the case. I feel the main reason was fear, due to the fact that the people of these lands had never seen a white person and such advanced weapons before. Until Sept. of 1492, a white man had never walked these lands, so when the Natives first sited these people they looked at them as gods. To these "gods", the Indians would give items such as gold, spears, cotton, and jewelry at their command. The Spaniards were really greedy though, and this was indeed not enough to bring back to King Fernando and Queen Isabel, who were expecting silk and gold from the Indies, so when the gold was not found much of the Spanish's profit was taken from the Indians by force.
The Indians attempted to save their lives from the Spaniards who used to cut their bodies in pieces to test the sharpness of their blades, but there spears and knives were no match to the gun powdered weapons of Europe so they had no choice but to let the Spaniards do as they pleased just so they wouldn't kill off more of there people. For this I feel that the Indians, unfortunately, did not have any chance of resisting Spanish encroachment.