I think China/India will be world leaders in less than 40 years. Like Nobunga said though, they need to fix some problems with their population's quality of life to ensure the keep of the power (can we say that in that manner?

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But I just want to remind everyone that 2100 is in almost 100 years...
What nations were the world dominators at that time? England, France, Germany...Maybe they could've imagined USA would be a world leader in industries and military in 100 years, but they could've never thought about China or India...
Maybe well get something like "South-American Coalition of nations" rulimg the world in 100 yaers...it is a little too far to predict I think, a scale of 50 years is more in our sight.
Plus, if a world war is declared (wich could be a plausible option) its clouds our vision of the future even more! (Yoda would say it that way...lol)