Personally, I think once the US is gone and whatever happens afterwards happens, if history somehow remains accurate, I think people will see the last 75 years as a world-wide Pax America with the most benevolent world leadership that has ever existed. I'm sure I'll get downvoted to oblivion for this statement, but, big picture, the US has done more to provide peace and prosperity (and even freedom and justice) for a greater percentage of humanity than any other nation ever.
If you look over human history, the natural human state is generally oppression, warfare, starvation, and disease. We just might be reverting back to the mean.