Just war criterion is often too strict and struggles to justify any war. World War II; arguably the most justified and necessary war in all of history would struggle to be justified using a modern doctrine of just war. In the 21st Century the most problematic requirement of a just war is that only a legitimate political authority can wage a war. My point is best illustrated by a comparison between the September 11th attacks in 2001 and the bombing of Pearl Harbour in 1941. I will discuss the attacks and demonstrate the problems that the distinction between the two highlights major flaws in the idea of legitimate political authority. I will then be able to discuss what can constitutes a legitimate political authority if a nation-state is no longer the reasonable definition. I will discuss Rawls’ political theory of an international overlapping consensus in his work The Law of Peoples allowing for a global conception of justice. My overall task is to define what should constitute a 21st Century legitimate political authority.