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The Quran and Muhammad talked about racial equality and justice as in The Farewell Sermon. Tribal and nationalistic differences were discouraged. But after Muhammad's passing, the old tribal differences between the Arabs started to resurface. Following the Roman–Persian Wars and the Byzantine–Sassanid Wars, deep rooted differences between Iraq, formally under the Persian Sassanid Empire, and Syria, formally under the Byzantine Empire, also existed. Each wanted the capital of the newly established Islamic State to be in their area. Previously, the second caliph Umar was very firm on the governors and his spies kept an eye on them. If he felt that a governor or a commander was becoming attracted to wealth, he had him removed from his position.

Who ruled Syria before it was conquered by the followers of Muhammad?
Byzantine Empire