With history !
one reason why the spanish easily conquered the americas was that the aztecs and incas lacked:
wealth and power
loyalty to their leaders
the will to fight to the death
resistance to european diseases

The Aztec and Incan people had never come in contact with the bacteria and germs the Spanish brought with them to The New World and so their immune systems did not have any specialized defense against them, this meant that the bacteria and germs the Spanish carried with them, while not being enough to affect the Spaniards, were practically overexposure for the Aztec and Incan people.

Yea where are the options?