The establishment of a territorial empire in the Americas by the Spanish was caused by the response of the Amerindian peoples. Their small tribes could not support each other and their isolation from other continents made the Amerindians susceptible to a more aggressive Spanish approach.
Thus, instead of cautiously developing a relationship with native peoples, the Spanish chose to overpower them. While, in Asia or Africa, native residents were able to enter into military conflicts with the Spanish or Portuguese to defend their independence, the Amerindians did not possess similar technology or strength to respond to sudden attacks. New territories were appealing to conquerors because they had not yet been explored by other countries, presenting an opportunity for finding new resources.