NATO bombed Belgrade not the US, because portions of the Serb army under the Milošević regime was carrying out well documented massacres and ethnic cleansing. That's why they stepped in. Yugoslavian aggression was halted and a UN peace keeping mission was put in place. Regardless of all this, carrying on as if all would be peaceful if not for the US is ridiculous. This conflict has been going on long before the US was even a thing.