"a declared war..." I thought that the idea of actually declaring war (except as a metaphor) was considered terribly old hat.

Not that I can see that a formal declaration of war makes much difference when it comes to the morality of saying "We will kill every single one of you until you stop doing what we don't want and do what we want - starting with all the people in this plane/building/city, to show that we mean what we say."

That's terrorism. To quote the definition in the dictionary I've just taken off my shelf: "Method of government by inspiring terror by acts of brutality and savagery".