Another book by David Weber. This is sort of the sequel to Insurrection, but actually takes place way before that one does.
It seems that he is using this universe to work out some ideas about politics and military might. This one deals with an attack by jihad minded aliens who have a different set of values about why they are fighting. So the human side has to think about why and how much and how much sacrifice risky missions are worth to save the other race. Because the easy answer is to destroy them all, but can we morally accept that?
I like the conflict between military and political sides. It is what happens in our own day. Perhaps Weber is a bit optimistic because all of his wars are won in the end. In our own day the wars sort of peter out as the political will driving them falters.
Crusade. David Weber & Steve White. Baen Books. 1992