The decline of the Roman empire was a wild thing for the people actually living on the ground. Imagine you're living in Alaska. You were born there and have never considered yourself anything but American. Your home is, as far as you're concerned, completely inseparable from America and as American as any other part of the country.
One day you see an emergency press conference on the TV. It's a press conference by governor. They're announcing that they just received word from Washington. The message said:
"We're sorry we have to do this. But the federal government just can no longer maintain our presence in Alaska. The country just can't afford it anymore. The national finances are exhausted and the nation must consolidate down to focus on its core territories. You will no longer be federally taxed, all federal troops will be withdrawn from the state, no federal dollars will be spent on the state, and Alaska will no longer receive representation in Congress. Existing US citizens in Alaska will retain their citizenship, but new children born in Alaska will be subject to the same citizenship rules as those born to American expatriates living overseas. We are granting Alaska full independence. We wish you the best. Good luck. But you are on your own."
Imagine what it would be like to be a resident of Alaska and to hear that message. How do you even respond to that? Do you stay in the US, leave Alaska, and move to the lower 48? Do you try to stick it out in the newly independent Alaskan nation? Can Alaska even survive as an independent nation?
In the modern world, we're not used to national governments just packing up and leaving a state or province. Governments work so hard to suppress even the possibility of revolt that the idea of one just abandoning a state or territory is a strange concept. But historically this does happen with declining empires. It really wouldn't even be that crazy of a move for a declining US. Alaska is a part of the US, but it isn't a core territory. The lower 48 is really the core of the United States. Territories beyond this are mostly money sinks useful for either resource extraction or power projection. Nice things to have, but not the US's core population and economic centers. I can foresee future scenarios where the US eventually just walks away from places like Alaska, Hawaii, Puerto Rico, and other territories not contiguous with the US mainland. No empire lasts forever, and collapse tends to move from the periphery inward. On the ground in the periphery, this looks like the national government just announcing you're no longer part of the country.
