That will happen until you reach the 'optimal' level. We will probably reach that level once Madina plus Arnor die. If those realms don't die, then monsters will continue to hit them harder and harder until they break. Don't forget other realms that border monsters like Luria and Westgard. The same thing will happen to these realms until they die. Once enough realms die, people will be force to migrate. The only problem with this method is people quitting. If people rage quit en mass, the density will not rise thus forcing monsters to fight and kill more realms. You can only lose with this scenario. The best solution at this point is to abandon outer realms quickly and move inland.
