The law of the jungle is reality. World War II was won by terror bombing civilians. It is lamentable, but reality is reality. So to say "that's not how it works" is denying reality.
And you appear to believe this is a pretext for humans to ignore their own laws and commit atrocities, when they could choose otherwise.
It may be reality that jungle law is currently how humans almost always handle conflict at nation-state scale. Non sequitur that it should remain so.
> not how this works
When you say this, what exactly are you referring to?
This usually means weaker (militarily/economically) countries banding together to hopefully provide some dis-incentives for strong arming.
It only works until someone calls the bluff.