I give USA 60 more years. Once it runs out of water and starts stealing all the canadian resources, it will be in some economic super struggles xD
they wont run out of water...american carriers I heard have water purifying generators that can even purify sea water..I think the war will be on oil...they'll still have alot of money due to the unimaginable diamond veins/deposits in alaska
but like every empire it will end...it will not fall but lessen as a superpower.I bet china,canada lol, or one of the rich european countries will become the next superpower
but due to the resources us has...it'll b a lonnng time till it steps down