That's a good question. It depends on which colonizers - as there were many, from many different cultures. And even within one culture, colonizers could behave very differently. For example, Spanish colonizers tended to enslave the Natives or convert them to Christianity (or both), but some Spanish colonizers were against this and advocated for Native rights. Even the English differed on how they should interact with Natives - some were afraid, others saw trade opportunities, and still others just wanted to conquer or kill them. There are many answers, and I suggest reading some of the accounts of colonizers (you can find many of these documents online for free) to get a better sense of what happened.