The demise of some New World civilizations were due to the introduction of "blank" into the area. Their introduction of new diseases, such as "blank", wiped out most of the indigenous people. Then some civilizations were taken over by "blank" such as the Aztec's demise by Hernando Cortez and the Incas at the hand of "blank".

The correct answers are:

- diseases;

- smallpox;

- force;

- Francisco Pizarro;

Contrary to the popular belief that most of the indigenous people in the New World diminished in numbers was because of murder by the colonists, the fact is that most of them died because of the introduction of diseases that they were not immune to. Diseases like the common cold and the smallpox were fatal for the New World civilizations as their body was not familiar with them and had no defense mechanism.

There were also several New World civilizations that suffered because of war too, like the Aztecs and the Incas. They were attacked by the Spanish conquistadors who wanted to get to their gold and silver, and were not choosing ways in order to get to what they wanted. Some of the most famous conquistadors that were involved in these actions are Hernando Cortez and Francisco Pizarro.