Natural horsemanship isnt just riding without tack, I don't have quite enough time to explain it is depth but heres a quick answer.... Horsemanship I also groundwork, where the human 'speaks the horses langauge' instead of expecting the horse to speak the humans langauge. All hrose herds have a pecking order, The top horse in the pecking order gets to eat/drink first, and all those things. But they also are repsonsible for the herd, they keep watch for any trouble and if it comes to it they will fight off any threat to the herd. The human is supposed to be the top of the pecking order, If there is a clear pecking order btween the human and horse almost (or no) force is needed, and human and horse work in harmony.
That's all I can think of right now ;) I will post more when I have more time