Martial arts are pretty ineffective when you're opponent is in full plate armor :toughninja:
Tell that to the original inhabitants of Okinowa when the Japanese invaded.
Okinowan = mostly naked man with stick.
Japanese Samurai = man with armor and wicked sharp sword, or spear.
There were many, many dead samurai in that invasion.
Granted, I don't think that samurai armor counts a plate mail, but still, it was armor nontheless. Didn't help them too much anyways.