Shito-Ryu Karate Do is one of the 4 main styles of Karate, the other ones being Shotokan, Goju-Ryu and Wado-Ryu. Besides these 4 main styles there is a wide variety of other styles, system and family forms of Karate. All ot them trace their origin back to the island of Okinawa, formerly also know as the Ryukyu Islands, and the martial art developed there.
 The island of Okinawa is the main island of the Ryukyu group in the eastern part of the chinese sea. With China in the west, Taiwan in the southwest and Japan in the northeast it is building a bridge between China and Japan along which the chinese culture reached the japanese main islands. So the okinawian matial arts were mixed with different chinese stiles and became a proper system. Specially due to the ban of carrying weapons and the japanese occupation of Okinawa, this martial art was practiced in secret and developed into a wide variety of different family and village styles. 
All ot them trace their origin back to the island of Okinawa, formerly also know as the Ryukyu Islands, and the martial art developed there.