Now, Before you all get mad at me, think about it. The Grand Council of Skyrim Replaces the political power of the high king and gives it to the Jarls. They make the laws in their holds and run them autonomously except for when there is a matter that concerns the Whole of Skyrim. The Grand Council convenes over this matter and debates what to do. this would usually concern Diplomatic/Military.

thoughts, High King could be used to determine the head of the Council and the one who deals with the Diplomatic issues.