Apart from religious reasons, why were the Roman and Byzantine Empires separated and in constant war with each other?

Related Questions

• Should the British defenders of Singapore have turned guerilla rather than surrendering to the Japanese?
• Why didn't the British hide troops on the Malay peninsula and then attack the Japanese from the rear as they ...
• What was it like to work for the Red Cross in Nazi-occupied Europe during World War II?
• What role did the Soviet fleet play in WWII?
• In WWII, did the Germans keep the Soviet kolkhozes and state factories during their occupation of Ukraine and Western Russia?