TKD is a mixture of earlier Korean martial arts and Japanese arts like karate and jujitsu. The Japanese occupied Korea in the early part of the 20th century, and though the political situation was aggressive the influence of the martial arts was positive.
Unlike most martial arts Taekwondo was standardised in the generation after the Korean War (the late 1950s onward). Where most martial arts vary considerably between the various teachers and schools TKD is quite consistent.
Taekwondo is almost the only martial art at the Olympic (the other is Judo). The standardisation of the art in almost all countries is one on the major reasons why it can be practiced at the Olympic level (Other martial arts are scheduled for the upcoming Olympics).
North Korean Taekwondo exists, but it has a set of standards that are slightly different. Nobody it too sure on the extent of the differences, but it is enough to prevent them competing in the Olympics.
TKD is part of the military training in South Korea.
Unlike the Japanese martial arts that influenced it TKD emphasises Kicks. Many of the earlier martial arts emphasised strikes with the arm.
Even though the legs are emphasized TKD training includes effective blocks, punches, sweeps, throws and other techniques.
Like many leading martial arts there is a great deal of emphasis on the mental aspects of the practice. Many individuals find this the most beneficial aspect of the training. A good mindset allows more rapid progress in other areas, including physical fitness.
The injury rate of Taekwondo is lower than most other martial arts, especially mixed martial arts. However, injuries are more frequent than in other sports.