Prior to the advent of Columbus to the Americans in 1492, the Americas were populated by people to whom we commonly refer to them as Native Americans or American Indians. This means, of course, that when the colonization of the America mainland began, that these same people were already occupying it. The fact that the lands in America were occupied by native peoples, was certainly no impediment to the over arching plan of the European nations that saw America as truly a new land of opportunity and riches, rife with the possibilities of vital trade, colonization, and exploitation.
Not too surprisingly, there was from the inception of the Europeans landing upon America, a general unease between these two different cultures, to which each culture, no doubt, felt it was more entitled to these lands than the other. Additionally, the American Indians were impressed by the great ships that crossed the ocean in order to arrive in America, having absolutely no conception whatsoever, of how many more peoples and ships the Europeans had in their possession, which ultimately seemed to be unlimited.
Then too there was the important concept of dividing and conquering to which the Europeans were expert at this tactic, in which they remained united in principle, for the most part, even if there were deep divisions between European settlements, whereas American Indians were historically grouped into family-based tribes to which the friendship from one tribe to another was often fraught with some peril or bad blood between one and another. This division between different American Indian tribes was something that Europeans were able to exploit time after time as certain tribes believed in the concept that the enemy of my enemy is my friend, a decision that contributed to the American Indian's ultimate insignificance.
Additionally, the Europeans possessed firepower and arms that were completely foreign to the American Indian, in which these arms were far more effective in killing, giving the Europeans a massive edge in battles between the two rival groups. Also, the experience that the Europeans had in warfare was the type of experience that they were able to utilize in order to more effectively plan out and strategize their battle plans against the American Indians.
So too, it cannot be underestimated, that common diseases, that American Indians had no immunity against, such as smallpox and the measles, ended up killing and sickening an incredible number of American Indians, destroying and decimating many tribes and their peoples.
In addition, there were the endless treaties and agreements of understanding between European powers and the American Indians, to which these treaties were broken by the Europeans and their descendants time and time again, so that the Europeans pretty much got whatever they wanted, anytime that they wanted, without having to make any sort of real accommodation for the American Indians and their interests.
What the American Indian was completely unaware of was that their way of life, was under assault from virtually the first time that Europeans set foot upon their continent, to which the Europeans never honestly considered sharing this great land with these native peoples. The choices for the American Indiana were to assimilate themselves into the conquering nation, or to be annihilated, or for perpetual banishment.