How can we force the military to kill civilians?
As far as I know there is no way to have your military attack non manic dwarves. Really, this is a good thing (except in the case of nobles and children) because dwarves make friends and have families so killing one usually results in their friends and family rioting causing mass !!FUN!!. There are lots of other ways to dispose of unwanted civilians including (but not limited to) magma, forgotten beasts, danger rooms, swimming training, !!SCIENCE!!, etc. For more information, check the wiki under !!FUN!!.