Why were the military and civil powers split in the Late Roman Empire?

Question

The administration of the Dominate (aka Later Roman Empire) was different in many ways from the Principate (aka Early Roman Empire).

In most cases it is rather clear why the various reforms had to be made. For example, breaking up the provinces into smaller units was part of the overall bureacratization which was itself an expedient way of extracting more revenue from a bedraggled land and population to maintain larger armies (and a larger bureacracy to boot).

However, I don't quite understand why the civil and military parts of the administration were separated.

Answer 1

The main reason was to reduce the ability of a single man to raise an army and wield it against the Tetrarchs. An army commander had troops (and possibly a lot of them) but did not have the infrastructure to keep them fed and supplied if he revolted. Similarly, a disaffected governor had no troops to raise a revolt. So an internal revolt had to rely on the coordination of at least two disaffected men in the same area, and this gave a much smaller chance to happen and a much higher chance for discovery while the two planned than the previous method, where one man had wide civil and miliary powers at the same time.