alt Hacker NewsThe Roman state was arguably much more modern than the medieval kingdom. It was highly centralized and funded through taxation (most of the plundering was already done by the early imperial period).
Not sure the Huns were the biggest direct threat either (unless we think that they are directly responsible for the Gothic migrations/invasions who were the ones who took over significant parts of the empire).
The "taxation" point is arguable since so much of it occurred in the provinces and basically amounted to plunder. Also, centralization is not much of a marker of modernity: the Ancient Near East had large centralized empires, but they were also similarly vulnerable to collapse for practically the same structural reasons; we just know a lot less about those times and places because the sources are so much more sparse and understudied.