[stripes1776]

Absolutely not. The empire was administratively split by Diocletian in the 3rd Century CE. Theodosius was the last empire of a unified Roman Empire and it irrevocable split in 395 CE.

Theodosius was not the last emperor of a united Roman empire. You are omitting Constantine and Constantius II and Julian the Apostate.

Constantine defeated all of his rivals and united all of the Roman Empire under his single rule. He then moved the capital from Rome to Constantinople, naming it after himself. Constantinople was the imperial capital of the entire Roman Empire under the sole imperium of Constantine. After Constatine's death the imperium passed to Constantinius II, and after Constantinius II to Julian the Apostate. After Julian came Valentinian. It was Valentinian who set up his brother Valens as coruler.

The weakness of Constantinople became evident fairly soon after the death of Constantine, sole emperor of the Roman Empire.

[rmlew]

Theodosius died in 395 CE. The YOu are confusing him with Diocletian.