If that is the main issue, the solution is easy: Limit the number of regions that realms can absorb in a short time, irrespective of realm size. So if you can only take 1 or 2 regions before half your realm blows up in unrest, you'd go for peace after that, and ready for the next war to take another 1-2 regions.
How would people circumvent this (because I know they will) ?
