Getting right down to the most primal purpose of war, it's about:
1. territory
2. wimmins
3. resources for keeping wimmins and the progeny you get 'em pregnant with. (This is a subset of "territory.")

War and things martial are a male institution. However, war is both In/Yin and Yo/Yang:
1. In/Yin: Defending your territory/wimmins/resources against invaders who want your territory/wimmins/resources.
2. Yo/Yang: Invading someone else's territory in order to take said territory, their wimmins and resources. This can be done by overt force and taking, or by "diplomatic negotiating" when one is in the superior position and offers "diplomatic" solutions. Nevertheless, it is conquest.

This has not changed since the dawn of human settlement.

We can plaster on layers of nuance and sophistication, but it after all the fancy wrappings are peeled off, it still comes down to the above.

So, in defining "martial" as regards the "martial arts," in civilized societies, we are either just playing a game of symbolic militarism, or we are training for "self-defense," which goes back to the intial purpos of things martial (see In/Yin aspects, above).

We can apply rationale and romanticism or nobility to all of this, of course, including the "spiritual" angle of training to a level of expertise that give us the power to be generous and merciful to others -- withholding the sword from a posiition of power, rather than relinquishing the sword out of weakness.