"I charge your liege as his own sovereign Istvan. The Golden Bull gives him the freedom to not follow me outside our borders but the defence of my Realm is still mandatory for all the nobles that I have granted lands and titles to. Bokeny has been entrusted to be Lord Privy Seal I expect more from him as Junior King than to squabble with mine own vassal. Mikan is a capable general and his armies are sufficient, you may ask him to lend you some men for a particular battle if such a thing becomes necessary, though he has a good head on his shoulders and I trust him with taking care of the details in a good manner."

Spoiler Alert, click show to read: 
The rules of the game state that the nobles own their land because otherwise it would be very dull to play in a game where one guy acts all high and mighty and everyone else does his bidding. Historically however the King owned all the land that was not part of the Church's property and in turn gave it out to the nobles in return for allegiance and knights. They in turn split their lands in smaller portions, leaving some for their private estates and granting the rest to their knights in exchange for service and so that the knights may pay for their destriers, mail and weapons. The knights in turn leased the land to serfs who toiled and gave a large portion of the produced goods back to the knight or just paid him a tax in gold form the sales they made. The rest they used to feed themselves and make a living. However ultimately the King still owed all of the land in the Kingdom and could revoke titles, confiscate lands and promote new nobles on a whim. Doing this in a game will suck however, but this was the reality back then.