"This happened: A starts a war W with B. As a follow on effect, some groups inside B starts a civil war W2 with others in B. You say that A is responsible for

"This happened: A starts a war W with B. As a follow on effect, some groups inside B starts a civil war W2 with others in B. You say that A is responsible for the second war W2 too, which they didn't start and even actively tried to stop?!" Well, let's see, the argument at Nuremberg was that Germany invaded Poland and sought diplomatic efforts to avoid conflicts with Britain and France, but those two attacked them over the invasion of Poland, which was Germany's war of aggression. So, it seems to me that if Germany was in a war of aggression against Britain, then the same applies to the US being in a war of aggression against the insurgents.