The US does it selectively. They literally sanction outside parties even looking into their war crimes. The war crimes the US acticevely punishes to a decent extent are convenient ones. My Lai? Couple of years house arrest for ONE guy. Abu Gharib? Extremely light sentences. Eddie Gallagher? Presidential pardon.

If you'd ever seen the aftermath of what they did at My Lai that "punishment" should sicken you. Hundreds of children raped and mutilated. An entire village massacred out of sheer bloodlust. And a couple of years house arrest (which caused outrage among the US populace, not the leniency but that any punishment happened at all)