I think the point they are trying to hint at is that it makes sense to try and understand the emergent forces that culminate in events as horrific as war.

You may "not believe in national interests" but something closely resembling that is a force governing social behavior.

So while it is important to pass moral judgements on these phenomena, you will be more effective at doing so if you can abstractly evaluate them absent moral judgement. Just as you couldn't coherently understand an ecology if you cannot accept obligate predators as a concept because of the moral implications of predation.

We will all differ in our moral and strategic assessments, but we all cohabit the same world, in which we can all recognize common truths arising from nature.