IntimateEvolution is right: there was an apocalyptic death rate in the years between first contact between Europeans and Americans and the settlement at Plymouth, and this was almost entirely due to disease. Nobody really knows how many people died, but it was a heck of a lot, and many more than we used to think.
Lots of modern Americans believe that the continent was largely empty and ready for settling. Well, yeah, it was pretty empty, but that was because the people who lived there had mostly died of smallpox and other diseases over the previous 50-75 years or so. Before those diseases hit, however, historians and archeologists now believe that the continent was much more densely populated. It's important to note that this is nobody's fault: nobody knew what the heck a germ was, and it's not like the Europeans went around deliberately sneezing on everybody in America.
Of course, many Europeans did take the (relatively) sudden depopulation of America as a Sign from God (tm) that the New World was ordained to be theirs for the taking, which probably played a part in the deliberate genocide(s) that happened much later, and we don't really know how many people were killed as a result of those policies, either. But it was a lot.
As for early wars between Native Americans and European settlers, some of us need to do some more research. Pontiac's uprising, for example, was hardly unprovoked. And if you look up the Pequot war, you'll find that the brutality of the English colonists (they burned down a Pequot village with the inhabitants in it, and shot anyone who tried to escape) was so horrifying to their Narragansett and Mohegan allies that they refused to fight alongside the English any more, saying that their way of war "... is too furious and slays too many people." Who were the real savages?