I've been thinking about martial arts a decent bit recently, as I've been getting more into HEMA (Historical European Martial Arts). There is no living tradition to learn from, but what is interesting is the fundamental difference between the way that Eastern martial arts are practiced and the way that HEMA is practiced.
Martial arts are fundamentally the arts of war. This is the art of killing, controlling, and dominating other people, on all scales. At the smallest scale, it is killing, controlling, or dominating a single person. On the largest scale, it is total war, and all of the skills that go into waging war on that scale. This will include the strategy of the generals, the defense of the supply lines, and the engagements with the enemy.
Martial arts are distinct from self-defense, though that distinction has been blurred with many of the modern schools. Self-defense is just the skills and techniques used to survive in the face of aggression. There is significant overlap, but the goals are fundamentally different. Self preservation is the primary goal of self defense, not the domination of another person.
In my view, the military organizations practice the purest form of martial arts. They train to wage war, and that is their fundamental purpose. Eastern martial arts like Karate, Kung Fu, and Tae Kwon Do are martial traditions, but they are not the most modern form of the art. The most modern martial art is fighting with firearms primarily, and unarmed and knife combat secondarily. This is in contrast with how martial arts are usually viewed, as it is seen as unarmed primarily, and weapons are considered secondary, or at least more advanced.
HEMA is interesting to me, partly because it has the different perspective on weapons. HEMA shares the military perspective, and weapons were primary, and unarmed techniques are secondary, though that could be an artifact of how we practice it in the modern case. I would not be surprised if that is was happened historically though, since it was relatively common to carry sidearms like swords and bucklers, messers and the like. Compare this to the development of the Asian martial arts, which were ususually developed as methods for peasants to fight using farming implements, since the regimes would not allow the possession of weapons by the populace.
But that is another topic. Why is the philosophy of martial arts so important (and often emphasized by practitioners) when it is fundamentally about killing people? I think it might have originated as a way to become less threatening. Anyone who has studied martial arts knows how fragile the human body is to unexpected attack, especially when weapons are involved. If you are considered a threat to a large number of people, then the chance that you will be assassinated goes up. There is also a strong disincentive to teaching people who would use the techniques to kill the teacher, obviously. I think these pressures might have contributed to the ties of martial arts with codes of conduct, honor, and morality.
When studying the martial arts, it is important to consider the philosophy that accompanies it. Why are we learning to kill and control people? When is it acceptable to do so? Are there causes that it is more important to kill than to save? When and why? I don't have good definitive answers to all of those questions yet, but it is important to start thinking about before a situation comes up and you have to justify the answer after the fact.