Indeed, and that's an important distinction.
Just war [0] proponents will argue both. For instance, targeting civilians/civilian infrastructure is gravely immoral (the decimation part), but also any armed conflict is unlikely to be successful and thus would be immoral on the grounds that there is no reasonable chance of success (the conquer part). But frankly, in this case, we don't even meet most jus ad bellum criteria, let along jus in bello.