I think part of the point is, they're running out of regions where an enemy can reside...
However, I think you're actually right. What is most likely to happen in a situation like this (especially if the people in charge of CE, or similar monolithic empire-realm at the heart of such a bloc, are politically savvy and recognize the danger of complacency) is for some of the outlying realms—particularly those almost-most-recently added to the Empire—to be declared somehow in rebellion, and "reconquered." Repeat as needed to keep your populace in line.
We have always been at war with Eastasia.
