That's why ex: El Cid (a great knight/military commander in Spain) was a threat to King Alfonso. (Doubly so because El Cid is a local hero who could raise a combined Muslim+Catholic Army, while King Alfonso was Catholic only. El Cid actually comes from Al-Sayyid, the nickname the Muslim locals gave to El Cid )
This happened enough in the Catholic monarchies that I have to believe it's really just the shape of Monarchies. Like the King of the Franks King Charlemagne the Great is basically known for his military exploits, with Paladins (his royal guard) forever influencing future Europeans and creating the image of an ideal Holy Warrior.
Did I say military exploits? I mean spreading Catholicism to the pagan Saxons. By conquest. During the Dark and Middle Ages, they spread Catholicism the old fashioned way, with the sword.
I do believe that Kim Jong Um military Uncle was put to death as well, likely as court intrigue and a preventative measure to prevent a powerful well respected General from overstepping his king.
Kings are always worried about their generals. Or better yet, Kings are themselves a general to prove their divine authority.