I'm not asking for instant restoration. But this is a problem that is specific to these island regions. The vast majority of regions in the Far East, and every other continent, have other regions surrounding them on most or all sides. If they were devastated by war and by being rogue, they would get peasants immigrating in from several regions, as many as four or five. Six in some cases. Not one.
Isolation has it's advantages. Unfortunately, you also have to live with its drawbacks. If you get devastated, it will take a long time to restore, yes. But it's also much harder to devastate you to begin with. Most realms could theoretically be attacked on all sides. You can only be attacked via a choke point.
