Who strengthened and enlarged the roman government and divided the empire into two parts?

Answer 1

No one divided the Roman Empire into two parts. There was only one Roman Empire.

The emperor Diocletian subdivided the Empire into four administrative units, not two. He created the four praetorian prefectures of Galliae, Italia et Africa, Illyricum and Oriens as part of his creation of the tetrarchy (rule by four). He appointed fellow general Maximian as co-emperor. Maximian took overall control of the western part of the empire, while Diocletian took overall control of the eastern part. Then these two men became senior emperors (Augusti) with the creation of two junior emperors (Caesars) who were subordinates of the Augusti. The Caesars Constantius and Galerius took charge of Galliae and Illyricum respectively. Their task was to defend the troubled frontiers along the rivers Rhine and Danube respectively, which were under constant attack from outside. Maximian took charge of Italia et Africa and Diocletian took charge of Oriens.

The creation of rule by four men and in charge of four administrative units and a doubling in the number of provinces lead to a massive increase in the size of the imperial bureaucracy. This was also due to Diocletian increasing this bureaucracy's control of local affairs.

There are two terms, Eastern Roman Empire and Western Roman Empire, which have been coined by historians. The Romans did not use them. They only had one term: Roman Empire. Diocletian stressed that the Roman Empire was indivisible.