As an additional notion on the Magic Kingdom, some thoughts from Sun Tzu:
Ground the possession of which imports great advantage to either side, is contentious ground.
Ground on which each side has liberty of movement is open ground.
Ground which forms the key to three contiguous states, so that he who occupies it first has most of the Empire at his command, is a ground of intersecting highways.
On contentious ground, attack not. On open ground, do not try to block the enemy's way. On the ground of intersecting highways, join hands with your allies.
So, by Sun Tzu's lights, arguably Parson shouldn't start a war in the magic kingdom, nor interfere with free passage therein, but (most likely) see who the heck was responsible for his summoning and get some damn answers (and perhaps have THEM interfere... discreetly).
Of course, he needs to deal with Jetstone, first.
On the current situation:
Rapidity is the essence of war: take advantage of the enemy's unreadiness, make your way by unexpected routes, and attack unguarded spots.
Parson is the Perfect Warlord. King Slately is a target, but an obvious one; Tramennis guarding him is (idiot ball aside) an obvious choice. So, what other less obvious high-value targets remain unguarded?
...A portal is one of the defining characteristics of the existence of a side. What happens if on arrival at Jetstone, Parson immediately turns and attempts to destroy the Jetstone portal that he came in through?