> I suspect this would be considered a valid thesis by future historians if the United States had existed in relatively stable prosperity for hundreds of years

> I suspect this would be considered a valid thesis by future historians if the United States had existed in relatively stable prosperity for hundreds of years beforehand and the result of such changes was that the US reduced in power and wealth to the extent that it sat on the verge of succumbing to foreign invasion by the mid twenty-first century. But this isn't at all what happened with regards to the late Roman Empire. The Western Empire recovered substantially from the crisis of the second century. The administrative changes that were made weren't the root causes of what happened in the late 4th and 5th centuries; they were actually what allowed (most of) the 4th century to be such a success. It's also emphatically not true that the Roman Empire of, say, the 370s, "sat on the verge of succumbing to foreign invasion" (even if you accept the notion of "foreign," which doesn't really apply to Rome's military relationship with many of its "barbarian" neighbors).