What does Control of the Army mean during the Roman Empire and how did it effect Rome?

Answer 1

Generally speaking, a Roman emperor required the support and loyalty of the Roman armies in order to effectively govern and remain in office. The first part of the answer says Roman "armies". This is so because at various points in time during the history of the Roman Empire, not all of Rome's armies were in agreement with each other and with the emperor. This often created a degree of instability to the government of Rome. Bottom line is that to remain in office, an emperor knew that his base of power was in Rome's military. Despite the fact that this had to cause a degree of instability, the empire was a force within itself, and as emperors came and went, often by assassination, the embedded bureaucracy kept the government going. Taxes were collected, farming and mining and commercial activities moved along. Now in certain cases, the legions of a powerful general would find out that an emperor's personal protection army called the Praetorian Guard, which was headquartered in Rome, might assassinate the emperor they were sworn to protect. They would install a new emperor ( this is meant as an example only) and unless the legions in the field agreed with the action, Rome had a new emperor.

If, however, generals in the field controlling armies which were large ( the Praetorians were small in number compared to legions in the field) believed this assassination was without merit & they were loyal to the murdered emperor, a civil war might be the result. Roman history covers many centuries and circumstances of each emperor's rule were all different. So, with that in mind, I have given a general answer.