The Rise of a Superpower Rival in the Roman Case

In the Roman case, what happens is that you get a buildup of wealth close to but beyond the Roman formal frontier. On the basis of that wealth, you get the emergence of stronger local dynasts who build up their power in military terms. We also see the rise of a superpower rival in the Roman case with the rise of Persia in the third and fourth centuries. That too is a response to very aggressive Roman expansion. And Rome can't dominate them so easily. It's having to make deals with them which acknowledge some of their rights in certain ways by the fourth century. Those change the strategic balance of power and Rome is not able, in fact, to confront and defeat them anymore.