The economic and social disruption which will occur as the result of shifting climate patterns is more pressing. Couple that with the shifting demands for resources such as oil and water as the population increases and cheap labor transfers some wealth and there is a recipe for wars.
The US does not have the population to occupy all the countries it would like. Neither does it have the British skills for allowing native rule of it's colonies. Even those skills failed them.

It will lose every "war" in which it engages unless it does find the troops to keep incountry. We won't be occupied, but will be isolated and marginalized.

This is not a political post, has nothing to do with any political position it's simply a guess as to the outcome of forces operating on the human condition.