Emperor Diocletian instituted the Tetrarchy around 293 CE, a system of four rulers, to better manage the vast and crisis-ridden empire.

This system created a precedent for dividing the empire into eastern and western administrative halves.

In 330 CE, Emperor Constantine moved the imperial capital from Rome to the city of Byzantium, which he renamed Constantinople.

The move to Constantinople shifted the empire's center of gravity eastward, to a more prosperous and defensible location.

Over time, the two halves grew culturally distinct, with Latin remaining dominant in the West and Greek becoming the language of the East.

The formal and final division of the empire occurred in 395 CE after the death of Emperor Theodosius I, who left the empire to his two sons.

The Western Roman Empire, based in Italy, faced increasing economic problems and pressure from migrating Germanic tribes.

The Eastern Roman Empire, later known as the Byzantine Empire, was more urbanized, financially stable, and militarily secure.

The two halves were never formally reunited after the division in 395 CE.

This division set the two regions on separate historical paths, with the West collapsing in the 5th century while the East survived for another thousand years.