Why there was a clash of cultures between european settlers and aboriginal?

the west was the most power full for a long time and could anyone and take what they wanted , but if you look at history the same thing happened time and time again in the old world europe asia africa , but when the spanish found south america the natives did not have the thousands of years of technology sharing or immunity to diseases people from the old world did , apart from the Maori who where apparently the toughest people the british army ever fought and never really conquered