The War on Terror launched by the US against Islamic terrorist groups persisted through the Bush-Obama-Trump administrations for nearly 20 years before President Biden completely withdrew the US forces from Afghanistan by the end of August 2021. These military interventions are noticeable examples of American unilateralism in the Middle East. The War on Terror has been severely criticized by the global community as military actions without just cause and lacking grounds under international law. This research aims to critically evaluate the War on Terror in terms of legal and political theories of war now that twenty years of American unilateralism in the Middle East is over. In this article, the author examines other underlying reasons for, and the outcomes of, the war against terrorist groups. He will also suggest peaceful means to fundamentally resolve the Middle East conflict with a view to preventing war in other world regions.