To muddy the waters further - what if the definition of "ethical" itself changes based on who invents the technology and wins the conflict? Have you acted ethically if everyone left alive considers you evil, even if you were upholding your own moral code?

There are ample historical examples of this. In the United States, we consider property rights, progress, and industrialization to be advances and theft and trespassing to be crimes, but this value system was used to justify the dispossession, relocation, and eventual genocide of the Native Americans. I bet that if diseases had worked the other way and slaughtered the colonists rather than the native inhabitants, we'd be living under a very different value system. Similarly, if the South had won the Civil War slavery would likely be considered just & ethical, or if the Nazis had won WW2 Jews would be historical scum, rightfully exterminated, and white supremacy would be the natural order of things. These groups are considered morally abhorrent because we won, which lets us write the histories and gloss over American atrocities like the firebombing of Tokyo or atom bomb.