Aikido is a modern Japanese martial art that emphasizes harmony and the redirecting of an opponent's energy rather than meeting force with force. It was developed in the early 20th century by Morihei Ueshiba, known as O-Sensei, who is regarded as the founder of Aikido. The physical techniques of this art, primarily joint techniques and throws, derive from various "old style" ju-jitsu, most notably those of the Daito-ryu. However, the Founder felt that his system was unique in that it united the mind, body, and spirit of the practitioner in such a way to overcome an opponent without resorting to a clash of arms. Employing movement principles and concepts that are special to Aikido practices, he used old traditions to develop the art to become a dynamic part of modern society. In addition to the taijutsu (empty handed techniques) of these ryu, O'Sensei incorporated many principles, philosophies and body mechanics from various weapons arts, especially those of the sword and spear.