User blog comment:Zathronas/Speculative author: The Grimm and the next season/@comment-5217560-20141012061957/@comment-5217560-20141013061514

As I recall, the Anti-Kaiju wall was demolished. I'm not saying it's just the natural barriers that are protecting them. Like you said, they have developed a fighting force, high tech weapons, fortifications, etc. However, it is the natrual barriers that are a major force in repelling the Grimm. No matter how many weapons they have, or how many fortifications they have built, none of that will last too long against unstoppable and immeasurable wave of Grimm. Especially ancient, and very powerful Grimm. Moutain Glenn failed because it had no natrual barriers to protect its borders. Oobleck said this from the jump. With no barriers to hold off the Grimm, they could not build the necessary fortresses needed to establish a city.

Hmmmm I guess my point is, it's the natrual barriers that help keep the kingdoms established. When they crumble or if a way in is found out, maintaing the structure and security of the kingdoms will become nigh impossible. Makes me think of Attack on Titan a bit. Force is force.