[@Fabricant451] Hmmm. You actually gave me an idea. Lets say they all charge for the castle once they are all gathered. The streets empty, no guards in sight.
.
.
.
.
BAM
He gases them all. All the traitors killed in one fell swoop. He might massacre a good number of the population but do you think they would try that again? Maybe in a decades time but at least he got some time until the next gassing.

But I gotta say, I just forgot about the Rp and tried to make the perfect kingdom for Jack LOL. My model was completely unrealistic.
Ofc he has enemies in court but everyone is too scared to do anything. He rules through sheer terror and time to time gives some moderate rewards for exceptional behavior.
And 10 years of propaganda in the military, him being countless years on the front lines...at least he [b]must[/b] have the support of the military. He fought beside his men, he gave them speeches and so on. And the countless lives that were lost in the war? It wouldn't be hear to rile them up on pretext of their fallen brothers.
And him being there doesn't mean he is disconnected from his kingdom. In the occasion that he is locked up they won't just stand idle. Their life and their families are at risk too. None of the lords have personal guards of their own. They all belong to him.
But yeah, he has a lot of those who would rather see him gone, currently in control through terror.