That might be because it’s right: War is an instrument of politics just as taxation, law enforcement, welfare, or diplomacy. They are each employed to achieve political goals.

To a politician that should sound darn obvious because political goals is all they think about, it’s the generals and soldiers that need to be reminded of it because it influences the way war is fought, can be fought. As an example, in that rough section of the book (it’s been a while) Clausewitz goes on to explain how total war is impossible: For a people to have the will to fight they have to fight for something, and if there’s nothing to fight for, no civil life, no tradition, no nothing, only war, there is no will, any more. If fascists would read and understand him they’d realise why their politics, “war for war’s sake”, are inherently self-destructive. Difference between Stauffenberg and say Goering.