This will mostly be dedicated to Ninjas, the ancient class of Japanese warriors who are highly trained in the arts of Ninjitsu. Ninjas date back to the 1200, and Samurai even earlier. The Samurai were established as the nobility, and general warriors of Japan, sworn to protect the upper class mostly. Ninjas branched off of the Samurai after a general disatisfaction with the service. For more information on these awesome assassins, click hereOr, you can learn about the Samurai, even though they aren't cool guys.
And you can find out how the boom of martial arts started in America here