History of the East–West Schism
Disunion in the Roman Empire further contributed to disunion in the Church. The Emperor Diocletian famously divided the administration of the eastern and western portions of the Empire in the early 4th century, though subsequent leaders (including Constantine) aspired to and sometimes gained control of both regions. Theodosius the Great, who established Nicene Christianity as the official religion of the Roman Empire (see Edict of Thessalonica), was the last Emperor to rule over a united Roman Empire. Following his death in 395, the division into western and eastern halves, each for a few decades still under its own Emperor, was never reunited.
Kingdom of Arles
In 1365, Charles was the last emperor to be crowned King of Arles. In 1378, Charles appointed the Dauphin of France (later King Charles VI of France) as permanent Imperial vicar to administer nominally on behalf of the Empire what remained of Arelat, and from then on Arelat in effect ceased to exist. However, the title "King of Arles" remained one of the Holy Roman Emperor's subsidiary titles until the dissolution of the Empire in 1806, and the office of the Archbishop of Trier continued to act as an archchancellor and prince-elector for the King of the Romans (the designated future Holy Roman Emperor), a status that was confirmed by the Golden Bull of 1356.