It is widely believed that Jiu Jitsu originated in Japan by the medieval warriors of Japan - the Samurai. These were the Japanese equivalent to the European Knights. And like Knights the Samurai were men from noble families who dedicated their lives to the art(s) of war. The Samurai battled in armour with the conventional weapons of the time like swords, polearms, staff  etc. Jiu Jitsu is an art that was compatible with fighting in armour and against armoured opponents. Thus Jiu Jitsu was developed to gain advantage over an opponent. This caused the development of Jiu Jitsu to include locking, throwing and pinning techniques as well as the more common place kicking and striking techniques of other martial arts. With the use of these techniques an unarmed Samurai could effectivley defend himself against an armed (or unarmed) opponent. It is also a very effective none lethal method to use. Nowadays Brazilian Jiu Jitsu has eclipsed the style becoming the main body for us in the west.