Maybe if the civilian and high ranking officer were winking at eachother in the night when the enemy sent high end co opt eagles to pick off what remained. I don't understand what would make a country want to research and develope high end weapons of destruction if the R&D staff will then be at risk of these eagles.
There is no line. In every major conflict this century bombs have been dropped on towns and cities, what is the purpose of that other than to kill civilians? Let’s not even mention the only practice of nuclear war, which saw bombs dropped on civilian populations with no warning at all.
Your last sentence isn't entirely accurate. You should research Truman's warning to the Japanese prior to dropping the nukes. Also check out the "LeMay" pamphlets, dropped before both nukes to warn the Japanese that the bombings were coming. While warned something big was coming, the Japanese were not explicitly warned of the nuclear bomb. Even if they were explicitly warned, would the Japanese have believed the USA? Probably not. I doubt very many people would have understood the power and devastation these weapons would cause. Anyways, Chad, check out the Geneva Conventions. That's a good place to start. I am also pretty sure assassinations of foreign leaders is prohibited by US officials. Either Carter of Ford wrote an executive order after it was made public that the CIA had been plotting assassinations since its creation. This didn't sit well with the sitting president so the executive order was made.