Footnote
In discussing the idea that so many transgressions of the Law mandated in Torah (allegedly by God) result in punishment by death, my rabbi pointed out that a more accurate translation of that commandment is: "Thou shalt not murder."
I.e., justifiable homicide is already built in, whether or not an act of war. It conveniently allows for the rather bloodthirsty instructions (in Deuteronomy) to Joseph and his troops about what to do when they get to Canaan, as well as for numerous death penalties.
You're right, though... it's a shame that, somewhere along the way, the Hippocratic Oath wasn't more widely adopted.
"First: do no harm."