[Sudetenland]

Duh! Rome fell because the people lost interest in governing and became interested in what they could get out of government...as Juvenal said in his Satire X.

The people that once bestowed commands, consulships, legions, and all else, now concerns itself no more, and longs eagerly for just two things - bread and circuses!
Juvenal, Satires
Roman poet & satirist (55 AD - 127 AD)

[Monterrosa-24]

But still your quotation is hundreds of years before the final fall of Rome. The Western Empire survived into the 400s because it was still Roman. It fell when the peninsula was flooded with those who did not consider themselves Roman but yet had the defacto status of freemen.

Do we have more and more citizens who do not call themselves Americans?