As this essay goes we have come to believe that an explanation for the Iraq war cannot be found in either the rhetoric or the claim that it was a legally internationally sanctioned war under international law. This is a theory-testing study where we use a theoretical perspective in political science from the international relations studies; Realism is examined, we want to see if it can better explain why the United States invaded Iraq. The main problem in the essay is to identify the reasons why the Iraqi invasion became a fact. In the C-thesis, we go through the perspectives content in a detailed way and briefly describe its views. We have collected material both about the Iraqi invasion and about the theory we want to test. Based on our pre-understanding of the theories, we interpret the developments in Iraq and try to explain them. We have come to the conclusion that realism is very much relevant to our subject and argues for it well. In realism it is the state that is the main actor and concepts like anarchy, self-help, survival and balance of power can best explain USA:s actions. This essay focuses on the means it took (the bush-doctrine) to legitimize such an act, but the mainspring of this essay is how we can understand the reasoning USA must have had behind the decision to invade Iraq. We believe that a realistic approach is the best way to explain what led the US to invade Iraq and through this perspective we can across chosen concepts from Realism, categorize different events that might have had played a vital role in this matter that are relevant with our theoretic perspective.