When Diocletian took over Rome forcefully he split the empire into two parts. Maximian was given the Western part.
Explanation:
Before Diocletian had assumed control over Rome, the empire had been in disarray for nearly a century and had seen more than a dozen monarchs in two decades.
It had become obvious that the administration was incapable of handling such a huge empire and that dividing it would actually prove to be a better deal as the troops would not have to be stretched.
The ever increasing number of rebellions that had sprung up in the century of anarchy were greatly curbed by the two empires separately and the split profited the empire as a whole.
