The prophecy of the King of the North is an unusual one in the fact that we're still to this day not quite sure who that "King" is, and who these people of the North are.  There are a multitude of theories ranging from Russia to a revived Roman empire covering Europe that will be ruled by the AntiChrist.  While that can't be verified, we can be fairly certain that it's not Russia as they will be gutted and rendered impotent by the battle of Ez38.  So the theory of it being a revived Roman empire is the most likely candidate in this prophecy.  However, like most prophecies of the last days, events and players will become more obvious and better defined as we get closer to the date.  For now it's enough to know that this is coming, and that it will be a Tribulation period event, likely right before the 2nd coming.