In North Korea propaganda videos have long been a common (and often the only) form of entertainment. One of the more popular type of videos shows soldiers using tae kwon do (TKD) and other forms of martial arts to demonstrate the high degree of combat readiness the soldiers had achieved. Most of the martial arts moves shown in the propaganda videos (and live shows presenting the same material) are more theatrical than practical.
This sort of thing first appeared in China centuries ago as groups of performers, including some martial arts experts, went from village to village putting on shows for a living. This practice was adopted in Korea and by the 1940s a unique form of martial arts began appearing in these shows, TKD that was intended for self-defense and physical training. After World War II TKD was adopted in both north and south Korea as a “national sport” (and is now international and an Olympic event). Most American soldiers arriving in South Korea after the Korean War ended (in 1953) could not miss it as most South Koreas practiced TKD both for physical training and for protection. In the 1960s TKD was all the rage with young Koreans. U.S. soldiers were warned that Korean marines were fanatic about TKD and to be careful if you encountered one off duty who had been drinking and was alone (muscle memory and booze do not mix). There had been incidents (one involved a heavily damaged jeep). By the 1970s TV had spread to most of South Korea and that hurt TKD popularity a bit. While TKD remains widely popular in South Korea today fifty years ago it was a minor religion. The persistence of TKD is largely the result of its heavy use in the military in both Koreas.
Eventually the use of TKD spread to the U.S. military. Many American troops who were stationed in South Korea during the last sixty years learned some TKD. In 2004 the U.S. Army revised its Basic Combat Training (BCT) course to better prepare its soldiers for 21st century war and incorporated more martial arts material. The new training included more emphasis on unconventional conflicts including non-lethal confrontation. Thus the new hand-to-hand combat techniques incorporated almost no killing techniques. The new program is a combination of Brazilian Jiu-Jitsu, boxing, and TKD. The U.S. Marines had a similar program, but their version included more killing techniques.
Since its original development in the 1940s Korean practitioners of TKD have developed more lethal moves. This came about largely because TKD was heavily used in the military. Both Koreas still have conscription (two years in the south, six in the north) and because North Korean young men spend more time in uniform they become more adept at TKD. In the last decade, as a market economy has developed in North Korea there is more crime and young men who have recently completed their military service find they can get jobs as security guards because their TKDs skills are in good shape.
North Korean soldiers are also better at TKD because in addition to being in the military longer, the North Korean forces have much less money than in South Korea for training, fuel and ammunition. So North Korean soldiers spend more time practicing their TKD since the government up there cannot afford much else. For all that TKD is not much use in combat. Instances of hand-to-hand combat are rare in modern combat, so North Korean troops would have little opportunity to practice their superior TKD skills.