What were the motives of the Spanish conquistadors?
Frankly, I think that the motives of the conquistador lies in their name. These men wanted to conquer "the other," that which was in front of them. They did not come in peaceful harmony. Their motives were to conquer and capture that which existed in their path to extolling their own glory, and that of nation in a secondary capacity. The Conquistador use of force through the military reveals that their motives were to control new lands and native populations. The exposure of native populations to new diseases from Europe such as smallpox helped in this process of control and subjugation. Conquistadors recognized that the lack of immunity to these diseases were withering resistance to the desires of the Conquistadors and what disease could not finish, the use of military force did. In this, the motives of the Conquistador became quite clear. The deception of indigenous tribal leaders into believing that the conquistador was an agent of peace only further enhances the motive of self- interest and destruction of "the other," supplanting it with their own vision of control and power.
The conquistadors had many motives, and of course different people surely had different motives. Overall, though, the typical conquistador was most likely driven by a desire to get wealth and power.
Many of the Spanish conquistadors were men who did not have a great deal of status back at home. They came to the New World in hopes of making their fortunes. They hoped, for example, that they might be given encomiendas, which were estates that they could run using the natives as essentially their slave labor. By coming to the New World, men like Hernan Cortes hoped to become wealthy and important in the new colonies that they hoped to take.