The event has your marshal asking you to appoint someone as a commander. This can trigger whenever you have empty commander slots available. First, the marshal will ask you to appoint any friends he has with a minimum martial requirement of 9, after that he will look for any dynasty members. If he has neither of those, he will try to ask you to appoint a commander with as a high martial skill as possible.
I hope that clarifies how the event works.
I hope that clarifies how the event works.