Right, the question is precisely this: who would leave the juicy morsel of Americas on the table in the 15th-20th century historic range. The means and processes may possibly vary.

Just to be clear, even today in 21st you will note there are many global actors that deny the very notion of a "universal human rights". I'm not European myself and definitely not defending what happened. But it seems to me that what happened is an (inevitable) accident of history: two worlds that evolved in effective isolation for thousands of years. And I wonder: which of the relatively advanced societies would have left them in peace so they could catch up and integrate as you propose?