After the death of Marcus, Diocletian (285-305CE) divided the empire into 2(285CE). The Eastern (Byzantine) empire, and the Western (Roman) empire.
Constantine (312-337 CE) moved the capitol to Byzantine. He did not oppose christianity and his mother and himself converted to it during their life times. Making him the first Emperor to do so. He died shortly after converting.
Justinian (527-565 CE) was a powerful Western ruler and attempted to reunite the empires but it did not last long. the plague of Justinian left the empire sick but soon to recover and left the empire itself recovering for 100's of years.
Some of the economic reasons that empires fell were the gap between the rich and poor, people that couldn't afford goods, and large estates becoming self efficient. Amries were not loyal to Rome, they were loyal to the emperors they were ruled under. The political reasons the empires fell were the decline in patriotism, slipped between the empire, and no orderly succession.
Down fall of the Empires
The social reasons the empires fell were because of the population decrease due to the plague, hunger, and war. The decrease in dedicstion to the public works and learning replaced by entertainment. Along with the religious beliefs that help divide the empires. Eastern and Egyptian cults destoryed the Roman religion, and new faiths like christianity questioned the concepts of divinity.
End of the empires
The Western Empire ended in 476 CE when Augustus was deposed by a Barbarian. The Eastern empire lasted until 1453 when it was conquered by Ottoman turks.
After the fall, I believe the Western empire will struggle a lot with everything mentioned and they will eventually get taken over by other successors, and the people who settled there will leave to find better sanctuary.