So what was america's punishment for knowingly and willingly killing all those innocents in hiroshima and nagasaki? Vietnam? Korea? The entire middle east. History is written by the victors, and surprise surprise, the actions of the victors are always justified as "the greater good" and everyone walks away.
But no, you are right, 50 years on a handful of people involved in mass genocides have been punished........while in their 90s. Murder is illegal too, does that mean you think it isn't extremely common? What about speeding, that's also illegal, but doesn't stop people from doing it. And if you think the dictionary definition of war talks about it being a fair fight between willing participants, you are in for a surprise.
Long story short, you are wrong.