Many people today have trouble understanding why European colonizers treated Natives of the Americas so cruelly for centuries that bishops, popes, churches, and national governments since then have apologized.
     Most Europeans were Catholics when the New World was discovered in 1492. Greed and racism were huge factors, of course, and so was the so-called "Doctrine of Discovery" that insisted rulers of developed countries had the right to do whatever they wanted in extracting wealth and conquering people of less developed countries. This is still true to a major extent today. Also, centuries of unyielding Catholic dogma during the 1500s and 1600s in favor of slavery and in condemnation of non-Christians (often labelled as "idolators") combined to created fanaticism by Europeans. In later years, the desire by many Catholic and Protestant religions to convert Natives added to the problem.
     Among the many reasons so many colonists acted the way they did include:

     * The practice of primogeniture in Spain and several other countries, in which in first-born sons inherited everything, resulting in the disinheritance of second-born and later sons who were accustomed to wealth. These disinherited Europeans then did whatever they needed to do to easily reclaim wealth and position in the Amercas.
     * The impecunious peasantry that existed for nearly everyone else in Europe, which motivated commoners to go to exrremes in the New World to elevate themselves from poverty and become rich.
     * Also,  the need of Spain and other European states for great amounts of gold and silver to finance the wars constantly sweepng across Europse.