When Rome Fell, the Chief Culprits Were Climate and Disease. Sound Familiar?
The chief culprit was permitting tens of thousands of barbarians to enter the empire.  They never integrated or left.  Within a hundred years, the western part of the empire collapsed.  <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Gothic_War_(376–382)" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Gothic_War_(376–382)</a>