Originaly heels were worn so that a horse rider's heel would not slip. The heeled shoe was then issued and used by all military around the 1600s because they all rode on horse back. The French royalty and military officers would wear them as part of their uniform. The men actually wore them at first but women started to wear them to look taller and more elegant. French men did wear some questionalble attire back in the olden days. If you have looked at some old paintings you can see the little heels on men.
I don't know who invented them, but apparently heels help tone your calf muscles. Definitely not worth the pain in your back, though, haha. I can't walk in stilettos or anything that's too high. It's the perfect recipe for me to fall flat on my face.