Could you imagine the future when there is no United States? If yes, then do you think you can guess how the US would cease to be?
Yes. The US will collapse through Balkanization.
Well, you could always wait a couple of billion years for the sun to incinerate the Earth. But the North American continent itself will not last more than one or two hundred million years due to plate tectonics. You won’t have to wait nearly that long for an ice age glacier to wipe out most of the country. ...and there’s so many other catastrophic ways to bring the USA to an end in less than a thousand years. The USA will end at some point, it’s up to us to make sure that the ‘natural’ end is what does it in. ...not ourselves!
The death of democracy
Democrats will cause the end of America.