User blog comment:SomeoneYouUsedToKnow/SYUTK's V4E10 - Guroyuri - Impressions/Recap/@comment-144.96.59.61-20170123171150/@comment-25936766-20170123214545

I think Kuroyuri did have walls...big ones. Granted, it didn't have a gate to close it fully, but still.

That said, they're not Kingdoms. They don't have the resources or the money to build titanic walls or heavy defensive weaponry. And even if they do, they generally don't have the forces to persevere while they're being built.