>>512887182
Rome fell becuase it dissolved itself into diversity. There is an excellent article referenced in picrel about the change in Y haplogroup as the empire collapsed.

By the year 200 AD, Rome was the largest and most cosmopolitan city of its time. As the empire’s capital, it was a magnet for people from all over the Mediterranean world and beyond, and its population was diverse and fluid. In addition to the vast number of immigrants, all Roman sources indicate that between 30 and 40 percent of the city’s population of over one million were slaves.

These slaves, drawn from every part of the Empire, included significant numbers of non-Europeans, from the Middle East, North Africa and sub-Saharan Africa, as the Roman records definitively show.

It was downhill from there. Emperor Caracalla (211-217 AD) issued the Constitutio Antoniniana (Antonine Constitution) – giving Roman Citizenship to all free men in the Roman Empire. Now anyone could become a Roman just by living (or immigrating) there. (Sound familiar?)

As is common with countries or regions comprised of racially diverse or mutt populations, Rome could no longer defend herself.

Roma, quid fecisti filiis tuis?

The only reason the Northern part remained relatively more white was the repeated barbarian invasions from there.