Complex sentence: The Byzantine frontier, however, began to be threatened by Bulgarian hordes; and so the Empress Zoe Karbonopsina sent two ambassadors to Baghdad with the view of securing an armistice, and arranging for the ransom of the Muslim prisoners.
Split into simpler sentences: The Byzantine frontier, however, began to be threatened by Bulgarian hordes. So the Byzantine Empress Zoe Karbonopsina sent two ambassadors to Baghdad with the view of securing an armistice and arranging for the ransom of the Muslim prisoners.