OTL, after the fall of Rome in 476, while the Goths had the northern portion, the Patriarch of Rome quickly contacted the Eastern roman empire and asked for their protection. While they were there they also took southern italy, just in case. However, this ended any ideas that the spiritual leadership was ever comparable to the emperor.
Your goal is to make the Roman church an important political institution distinct from Constantinople and Orthodoxy
Your goal is to make the Roman church an important political institution distinct from Constantinople and Orthodoxy