U.S invasion of iraq 2003 linked to one of the 3 major theories in international relations ( realism , marxism or liberalism)

Combining theory and practice of international relations and conflicts, you are required to focus on one major IR theory (e.g.: realism, liberalism, Marxism ) like one of those theories to the event ( U.S invasion o f iraq in 2003 )  write a 2 pages essay about how is the theory connected to the event.