The oldest Korean martial arts were an amalgamation of unarmed combat styles developed by the three rival Korean Kingdoms of Goguryeo, Silla, and Baekje,  where young men were trained in unarmed combat techniques to develop strength, speed, and survival skills. The most popular of these techniques was ssireum and subak, with taekkyeon being the most popular of the components of subak. The Northern Goguryeo kingdom was a dominant force in Northern Korea and North Eastern China prior to the 1st century CE, and again from the 3rd century to the 6th century. Before the fall of the Goguryeo Dynasty in the 6th century, the Shilla Kingdom asked for help in training its people for defense against pirate invasions. During this time a few select Silla warriors were given training in taekkyeon by the early masters from Goguryeo. These Shilla warriors then became known as the Hwarang. The Hwarang set up a military academy for the sons of royalty in Silla called Hwarang-do, which means “the way of flowering manhood.” The Hwarang studied taekkyeon, history, Confucian philosophy, ethics, Buddhist morality, social skills, and military tactics. The guiding principles of the Hwarang warriors were based on Won Gwang’s five codes of human conduct and included loyalty, filial duty, trustworthiness, valor, and justice. 
In spite of Korea’s rich history of ancient and martial arts, Korean martial arts faded during the late Joseon Dynasty. Korean society became highly centralized under Korean Confucianism, and martial arts were poorly regarded in a society whose ideals were epitomized by its scholar-kings.  Formal practices of traditional martial arts such as subak and taekkyeon were reserved for sanctioned military uses. However, taekkyeon persisted into the 19th century as a folk game during the May-Dano festival, and was still taught as the formal military martial art throughout the Joseon Dynasty.
Early progenitors of taekwondo – the founders of the nine original kwans – who were able to study in Japan were exposed to Japanese martial arts, including karate, judo, and kendo, while others were exposed to the martial arts of China and Manchuria, as well as to the indigenous Korean martial art of taekkyeon.    Hwang Kee founder of Moo Duk Kwan, further incorporated elements of Korean Gwonbeop from the Muye Dobo Tongji into the style that eventually became Tang Soo Do.
This information, and more about Taekwondo, can be found at the following Wikipedia link; http://en.wikipedia.org/wiki/Taekwondo