The Koryo dynasty, which reunified the Korean peninsula after Shilla (A.D. 918 to 1392), had the Taekkyon develop more systematically and made it a compulsory subject in the examinations for selection of military cadets.
The techniques and power of Taekkyon grew to become effective weapons even to kill human beings. In the military, a pattern of collective practice, called "obyong-subak-hui (5 soldier's Taekkyon play), was introduced so that it might be used in a real war.
In the early days of Koryo dynasty, martial art abilities were the only required qualifications to become military personnel because the kingdom utterly needed the national defense capabilities after conquering the peninsula. A certain plain soldier who mastered Taekkyon techniques was promoted to a general, and young were invited to Taekkyon contests where the skilled ones were selected to become military officers. There were lots of other examples in which many Taekkyon-mastered youths were picked at contests, which is proof that Taekwondo sports was originated in that epoch. The chronicles of Koryo dynasty writes: "at a power contest of Taekkyon techniques, Lee Yi- Min punched a pillar of the house with his right-hand fist, then some of the props of the roof were shaken. Another Taekkyon practicer had his fist pierce through the clay-wall."
Especially the kings of Koryo dynasty were much interested in "subakhui" (Taekkyon contest), making it a compulsory course of military training. Therefore, subakhui was also popular out for inspection tours in the villages.
However, the Koryo dynasty in its latest years had gunpowder and new types of weapons available at hand, thus slowing down its support of martial as the folk games to be transmitted down to the modern Korea, Chosun. (Taekkyon explained in the Koryo history book)
Courtesy of worldtaekwondofederation.net