Also more thoughts in the natural method you still strike the horse but in a constructive and positive manner..... its how when and where you "bite" or "kick"
Watch a herd in the pasture when the alpha mare wants to move someone lower on the pecking order
1: She Pins her ears back, cocks a leg and looks, or in human "MOVE"
2: She then bites the other horse on the rump or shoulder, or in human "I SAID MOVE"
3: She then may kick the offending herd member, or in human "MOVE AND I DON'T WARN TWICE"
Now as people we can't possibly kick the horse... so we have the lead rope with the leather popper on the end... that will in no way injure the horse, we are not capable of kicking or biting as hard as a horse and anyone who's been bit by a horse knows this.
As your horse progresses you ask with a gesture, then you add more pressure until they move their feet, these methods don't make the horse feel bad, they by nature are a herd animal and will dominate herd members they can't and vise versa... they as a rule accept their position in the herd and that position hopefully is below you in the pecking order
One thing to remember the horse is smart, is faster than you, out weighs you by several hundred pounds and has hard hooves and teeth, but with the proper treatment they will be the most loyal animal you have the privilege to be blessed with. (i'm sure the mustang would commit murder for me)