Well for starters the colonists were trying to take over the Native Americans' land and countries, which was made more conflicted by the fact that most Native Americans' ideas about land and countries were very different than the colonists'. The colonists also wanted the Native Americans to change religions and become Christian, which the Native Americans thought was rather silly and were perfectly happy with their own beliefs. The colonists also had a tendency to not care at all about the health or lives of the Natives, largely because the Natives were brown, and not Christian, and so the colonists were perfectly fine with simply killing Natives who got in the way of their plans, something which didn't go over too well with the Natives at all, and when the Natives fought back, the colonists promptly killed most of them, which they were able to do because they had guns, and the Natives, for the most part, didn't.