Not gonna lie, I kinda hate it. First no matter how random it truly is, the realm the gets attacked is going to say its rigged. Second it will cause the last couple realms to be attacked if you took all who had been attacked out of the drawing strong enough to ally and easily defend against the other realms because if your realm just got crushed it doesn't have much money to go attack a far off realm, plus they can't get their land back unless their neighbor is the next target because thats breaking the agreement thus crippling every realm that gets attacked. Third its completely ooc of character with no roleplay reasoning behind it, because what realm would be willing to have the entire continent attack them in real life. Fourth you force every realm to accept your terms since they would be breaking the agreement by not agreeing in the first place and get ganged up on.
