Question

What is a just war?

Answer 1

It's a theory that has been used to rationalize or define certain wars philosophically, such as those started as a last resort in self-defense when all non-violent options have been exhausted or to answer certain wrongs that require such a response but attempt to limit such fighting to only enemy combatants.

Some might consider the Allies' efforts in WW2 as a "just war" against the predatory ambitions of Germany and Japan, especially when atrocities such as the Holocaust became known later on.