This was the same time that Cassiodorus in Europe was reporting strange weather, a blue sun, a dim moon even when full no fruitful summer and no extremely cold winter. Just no change and no growth. A large boloid crash? A major volcanic event? But it did also seem to drive the steppe peoples out of central Asia, conquering or invading both East and West
David Key (or is it Keys?) put out a book, hmm, perhaps ten years ago, claiming that it was due to a volcano.