the commandment is not to murder. Murder and kill are not synonyms.
There is no difference between the two. Either way the victim is dead. Both
involve intentional killing. Both are really the same. There is a difference
between unintentional killing and intentional killing. War involves intentional
killing. The genocide of millions of Jews by the Nazis was "legal". So if you're
going to split hairs between "legal" and "illegal" killing, that is the same
as saying that the killing of millions of Jews was not a sin because based
on the law it couldn't really be called murder.