Are most South Americans of native or European descent?

North America is primarily populated by people of European descent, except for mexico

(which raises a second question, why is the USA and canada mainly European sescent while mexico is not, all three were European colonies but in Mexico, it was different)

I ask this question because you see countries like Argentina, uruguay etc that have many people of European descent, like North America. but then in countries like Brazil, it is the other way around.

Another Question, why did these different parts of the America's develop differently in regards to demographics and the population of people that have native descent? Why so small in Canada, USA, yet so large in Mexico and Brazil?
Additional Details
I thought I would ask this question here as well because much of the topics in the geography and the social groups section are dominated by the United States.

Thanks.