It's important to remember that mass killing =/= genocide. Yes, the Iraq Invasion led to mass destruction, chaos, and death, but what matters in genocide is intent. It was not with the intent to destroy Arab Iraqis as a social group, hence it was not genocide. Something can only be genocide if there was intent or, alternatively, that the actions taken would knowlingly deprive a social group of the conditions for life to the point where the social group would be destroyed (e.g., orchestrated famines, ontological destruction).

The US has plenty of other genocides to its name on its own continent, though, don't worry!