I often wondered why the Carolingian Empire of Charlemagne did not continue to flourish after his death. then I read a book about food which reported that in Europe in the 100 years after his death there were 33 famines some of which lasted 2 or 3 years. Examining my volcano encyclopedia I found several very large volcanic eruptions for that period, especially in the Far East. There was climate change in that period which caused Ergot of rye in northern Europe to kill many people, and in the south, Arab import of barberry bushes which is the alternate host to wheat rust plus climate decimated wheat crops. For the 540 event, Google Cassiodorus who may have described results of a major meteoric event, or perhaps a volcanic event.
Thanks gleeaikin. Always look forward to your interesting info.