The Byzantine Empire is the Roman Empire, or what remained in the East, after the West Roman Empire collapsed. Byzantines called themselves Romans as did the rest of Europe at the time.
- Christianity; It had been growing in popularity previous to Constintine’s decision and it would take some time to firmly take hold. But it did take hold.
- Population; The East Roman Empire had a larger urban population than the Western half. This allowed it to weather economic upheaval better than the other half of the empire. It also provided a better base to maintain a military.
- Greek language; Roman laws remained the law of the Empire. Latin remained common for several hundred years after the loss of the West. But there was and always had been a large Greek speaking population in the Eastern half of the Empire. Over time Greek became the dominant language.
- Feudalism; The Empire shifted to feudalism. This stabilized the labor force and created greater financial wealth than slave based work previously used.
- Political Stability; So the Empire changed to meet challenges over time. It adapted. Through it all, the line of succession remained. Sometimes the handoff of power was a bit messy but for the most part there was political stability. The stature and authority of the Emperors continued to grow.