For anyone that cares to read about how war is rationalized as being Good or Bad, go read up some
Just War Theory, which is the current doctrine for proper conduct prior, during, and after a war. It is the accepted rationalization of what is Just and Unjust in war.
As far as in-war conduct is concerned, the US went way more overboard when they nuked Japan (~200,000 civilian deaths) then when Japan attacked Pearl Harbor (60ish civilian deaths). You might be wondering why the US' attacks aren't considered an atrocity, essentially it falls into how desperate all the warring sides were back then to prevent their own losses.
War does not determine who is right, only who is left.
And everyone saying this or something like it should keep in mind that it is false. Each side's reasons for going to war will be scrutinized, and naturally you can have a good or a bad reason for doing things, it's the same deal for a war.