I think the biggest reason for the collapse of the empire is the failure to integrate immigrants such as the Germans and Goths. When they weren’t integrated they did massive amounts of damage to the empire. If they had been integrated the empire would have had many high quality soliders, and could had even had better men become emperors such as Stilicho, Alaric, or Theoderic.
Why did integration start to fail? I’m looking for a macro answer here and not just “the guy who let the goths in was a jackass.”
Let me know what you think.
The question might be flawed there, in the sense that the consensus rather goes to the idea Barbarians were integrated within Late Roman society, to various degree, and no longer that they were foreign elements.
It doesn't mean that they didn't have a distinct community identity (something remotely comparable to "hypenated-nationals") along with a distinct political definition, a Barbarian being whoever follows a Barbarian duke or petty-king.
The whole topic is still questioned, searched and debated about, but you mighty find some elements of response on earlier answers.
What was the Roman influence on Germanic peoples
What happened to the former Roman aristocracy in Western Rome after its collapse
Why are the spanish and french not considered Germanic
There's much, much, more to be said there and by other people; but I'd advise caution on the trope of "non-integrated Barbarians migrants" which is often less historical than political.