They use their economical and political power to enforce others to adopt their culture, values and religion. On top, they use their moral 'superiority' as an argument for their wars (where everyone has to support them) which is highly questionable.
Question is overbroad. Potential sub-issues to address: 1) what specific crime (worth differentiating whatever actions you're referring to), 2) can a country be responsible for a crime in the aggregate, or just the individuals responsible? 3) What punishment can feasibly be carried out?
they slaughtered tens of thousands of innocent people in Hiroshima and Nagasaki even though Japan was just about to surrender anyway. and the USA didn't get punished for it. and then the murdered lots of doctors and patients who did nothing wrong and nothing happened to the USA either.
America is responsible for thousands of deaths of both civilians and suspected terrorists in Afghanistan and Pakistan. Attacks on terrorists and suspected terrorists are carried out using armed drones. Whistleblowers have admitted that suspects above the age of 12! are considered targets.
The USA are running a world wide network of inofficial prisons, the existence of which has only been admitted in 2012. It is known that suspects have been transported to foreign or privately run organisations for further treatment, including torture.