We discussed the invasions of the Roman world by various Germanic tribes in the fifth century and the Arab-Islamic conquests of Persia, most of the Byzantine Empire, and much of the Mediterranean world in the seventh and eighth centuries. How did the new invaders manage to govern the advanced civilizations that they conquered?

The invaders were able to govern the more advanced civilizations because they adopted most of the conquered civilizations' customs, rules of governance, and even languages and religion.

For example, in the case of the Germanic tribes that conquered the Western Roman Empire, the rulers adopted, one by one, the religion of the Roman Empire: Christianity, more specifically, the Roman Catholic variant.

They also began to use the language of the Empire: Latin, for ecclessiastical and political matters, and while political institutions did change a lot, some of the political institutions of the Empire did survive in the sucessor states that the Germanic rulers carved out of the Roman territory.