I listened to the Fall of Rome podcast a while back, and there's a fascinating episode discussing what happened to Britain when supply chains started collapsing. Much like modern countries today, Rome relied on the economies of scale. Commodity production was centralized in different provinces, and then they would be exported across the empire. When the trade routes started breaking down due to lack of security and other problems, some provinces ended up being largely cut off from the rest of the empire and experienced rapid decline. British provinces in particular were hit hard and ended up regressing to subsistence farming within decades as their exports and imports collapsed.

While modern US empire is very different from Rome in many respects, I'd argue that supply chain risks are even higher than they were in Rome. Very few parts of the US can be said to be self sufficient, and millions of people living in large population centres rely on goods being shipped to them from across the world. What's worse is that the whole economy is organized around just in time supply chains with little to no local inventory. We saw how a single ship getting stuck in the Suez canal was a catastrophic event, this gives a bit of a preview of what can be expected on a much larger scale.