Why Rome's civil and military career balance weakened

How far was the later Roman Empire ruled by the military, and was it comparable to Cromwellian England?

Rome retained a mixed civil-military career system, but declining elite military participation and growing reliance on hired troops weakened it over time.

Roman elite service originally combined senatorial and civil advancement with military experience. As conquest slowed, military office offered fewer opportunities for wealth, slaves, and distinction. More people therefore concentrated on profitable civilian government while the state fielded fewer Roman troops and relied more heavily on hired forces. The answer treats that institutional shift as one contributor to western imperial decline rather than claiming that military rule alone would have solved Rome's problems.