The Roman Empire did not have a coup-d’-etat, no way. Rome was like the Soviets in the way that they crumbled on the inside, same with every empire, which is done in the way of Dark Ages (I think) in R&F.A state can collapse even without a war like the Roman Empire fell by a coup , or like the Soviet Union ended for internal reasons and the bankruptcy of the state , this should be simulated ! I am ready for discussion
For example, Spain once had the most powerful navy. In the 1980s, my history teacher had a friend who spent time in the Spanish “Navy” - Spain had only 2 military submarines - both of them were granted by the USA. One of them was actually functional, the other was junk and used as extra parts in case the first submarine was damaged.
What I’m trying to say here is that Civ already has this.