Ninjutsu, which literally means the art of perseverance, is a martial art system that focuses on unconventional warfare, strategy, and tactics. While the majority of ninjutsu ryuha (families) became organized during the Warring States (Sengoku Jidai) period of feudal Japan history, use of ninja spies dates back to roughly 560AD. During feudal Japan, ninja operatives were routinely used by many of the powerful warlords, while other ninjutsu families used their intelligence gathering skills to keep from falling victim to the land disputes and conquering armies trampling throughout much of the country.
Ninja operatives were routinely trained in a curriculum defined by eighteen skillsets:
Seishin-teki kyōkō (spiritual ref)
Bōjutsu (stick and staff fighting)
Shurikenjutsu (throwing shuriken)
Sōjutsu (spear fighting)
Naginatajutsu (naginata fighting)
Kusarigamajutsu (kusarigama fighting)
Kayakujutsu (pyrotechnics and explosives)
Hensōjutsu (disguise and impersonation)
Shinobi-iri (stealth and entering methods)
Sui-ren (water training)
Intonjutsu (escaping and concealment)
Taijutsu (Unarmed Combat)
Kenjutsu (sword fighting)
Ninja, rather than the cut-throat mindless assassins that poorly-researched movies purport, were far more similar to spies and special operations commandos that we see today. Highly-trained - physically, mentally, and spiritually - ninja were a tremendous asset and a fascinating evolution within the strict cultural confines of Japanese history.