The Byzantine Empire
The Byzantine Empire continued for over 1000 years till it was taken over by the Persians in1453. Constantine I made the city of Byzantium his capital and renamed it Constantinople, which later became Istanbul. In the early Byzantine period, Constantine converted to Christianity. Though successive kings attempted to reconquer the west, the region was under constant attack from the Persians in the east and the Germans in the west. Constantine however succeeded in controlling the anarchy that had prevailed earlier by making serious changes on administration like giving the emperor a divine status to insulate him from rebel forces and separating the civil and military authority. The economy also strengthened considerably.
In the middle Byzantine period, the Muslim Arabs, and the Slavs and Bulgarians posed threats to Anatolia. Serious disputes also arose over theological issues, which led to the ultimate separation of the Orthodox Roman Church and Roman Catholicism in 1054. New styles of church architecture emerged and a literary renaissance followed this separation.
However, the repeated Arab and Bulgar attacks caused the military and the civil authorities to be merged once again. In the 10th and 11th century, internal problems between the peasants and the land owners surfaced, and the emperors were so preoccupied with them that they were unable to prevent the entry of the Seljuks into Anatolia between 1048 and 1081.