As a result of the Empress Theodora's advice during the Nika Riots, Emperor Justinian

missouri compromise of 1820 which prohibited slavery

1. it was caused by feudalism

2. charlemagne used christianity as a major cornerstone for his rule. cloisters were built all over the empire to act as centers for the (re)population of the vast european wilderness.

3. the europeans feared the next raid every time chetak

i'm not so sure about #6. but i hope i you with the first 3.