1. Justinian accomplished rebuilding Constantinople after the Nika Revolt, constructing the famous Hagia Sophia church. He also reformed Roman law.
2. The split between the eastern and western churches was caused by theological differences and disputes over icons and the authority of the Pope.
3. The Byzantine Empire declined due to invasions by Muslim forces and Seljuk Turks, as well as internal weaknesses like the divide between the military and government. The empire was finally conquered by the Ottoman Turks in 1453.