You have just summarized the distinction between jus ad bellum and jus in bello from Just War Theory, which I would hope every military officer in the world understands.

...just war theory offers a series of principles that aim to retain a plausible moral framework for war. From the just war (justum bellum) tradition, theorists distinguish between the rules that govern the justice of war (jus ad bellum) from those that govern just and fair conduct in war (jus In bello) and the responsibility and accountability of warring parties after the war (jus post bellum).

Sadly I have observed many people do not make the distinction.