Read this: When their migratory movements ended, there appeared among the Slavs the first rudiments of state organizations, each headed by a prince with a treasury and a defense force. Moreover, it was the beginnings of class differentiation, and nobles pledged allegiance either to the Frankish/ Holy Roman Emperors or the Byzantine Emperors.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): What is another name for the Byzantine Emperors?
unanswerable