According to Humanist thinkers, political decisions should be based on

rational thought.

Explanation:

According to Humanist thinkers, political decisions should be based on rational thought.  It is because rational thought is based on the facts and with the help of these facts conclusion should be drawn. In politics, political decision should be taken by taking opinions of the members of the party. All the opinions should be considered by reviewing the facts and that opinion is selected for application on which maximum members of the party is agreed.

they died because of a disease during the first spanish colonies.