Sometimes I have seen it bemoaned that modern war is much more brutal toward "civilians" than ancient, medieval, or tribal war was. Yet, from what I have learned of warfare over the years, this seems to be rather backwards.
Tribal warfare consists and consisted of ritualized exchanges of violence away from the population centers of the conflicting sides, epitomized by the findings of anthropology of war in the Pacific Islands and 'akraticized' (double entendre) by the Archaic Greeks. This was of course not difficult in small tribal societies; in fact, anything otherwise was basically impossible unless a direct raid on enemy settlements or encampments was attempted, which would of course be a much risker enterprise. At any rate, this sort of small-scale skirmishing involved miniscule casualty rates and was more a matter of pomp and circumstance than anything resembling strategy or tactics. The last point to mention for tribal warfare was that if one tribe happened to overwhelm or rout the other somehow in one of these confrontations, the result was almost invariably total genocide or enslavement for the loser. It would be a rather grotesque and anachronistic quibble to discount this as a war tactic since 'it followed the conclusion of primary martial operations'.
In ancient and medieval (settled) societies with more expansive domains or areas of habitation, warfare was fundamentally centered around the use of terror against non-combatants. Why was this so? Because the scale and scope of war had increased, the risks of direct confrontation had grown exponentially. Even most victorious battles were essentially Pyrrhic ones for the winner, in that any serious losses to the main force, as well as the time consumed in operations, would tend to prove both logistically and politically expensive.
In other words: so-called "civilized" warfare up to the modern period was predicated on causing economic and moral damage to the opposition through denial of territory, devastation of territory, and devastation of non-combatants. Typically, warfare involved main forces maneuvering around each other and intimidating each other through displays of force. (The transient sieging of settlements was especially used in this regard during the Middle Ages).
Consider the success of the Romans. While this is not the whole picture, it is useful to highlight this point for the present context: They avoided the operational imperatives of the time to some extent by being able to rely on a relatively-large and diverse population base. The scale meant that losses were relatively cheap and easy to replace, while diversity allowed for shuffling of contingents such that enemy devastation of local non-combatants would not directly affect the personal lives of Roman soldiers to the expected extent.
Then, with the advent of national conscription (e.g. the Levee en Masse of Revolutionary France) increased the scale of war so drastically that set-piece battle became not only desirable but indispensable and unavoidable:
1. Losses are much cheaper to replace, but the size of the force makes it that much more difficult to maintain for extended periods. Thus, devastation becomes even more important as a means for the land forces to "live off the land".
2. The massive size of armies (now regularly in the hundreds of thousands) makes avoiding the enemy main force more challenging than simply finding the best time and place to confront it directly.
3. With whole "nations" morally, politically, and economically (esp. logistically) invested in the outcome, terrorizing non-combatants and therefore undermining armed forces and the governments responsible for them, becomes much more effective.
What changed with the World Wars was not the basic premise of terror against non-combatants, but technology and doctrine: you still had these massive numbers of troops, but their density declined such that battlefields could stretch almost continuously across entire continents. Our mistake has been to conflate brutality with scale and scope.
To round it off then, we must acknowledge that post-WW2 Western warfare has (at least momentarily) broken with the past in a tremendous way: military/state terrorism is widely condemned, and it has really practically vanished in the past generation.
Ultimately, this is merely a sketch of an argument, so please add to or criticize it. One could easily write whole books on the premise.
