>Who would exact punishment?

Vigilante "justice" of some kind.

> How would America etc even put Putin in jail?

Putin?

>I agree that awareness is good and that is what Geneva convention did. It wrote down what everyone already believed.

I'm thinking more about events in the last few decades. How many innocent dead people are there in the middle East as a consequence of US foreign policy?

>Enforcement seems impossible.

Dare to dream baby!