This is the final part of a three-episode series examining the post-9/11 world for the 20th anniversary of the al-Qaeda terrorist attacks.

At least 335,000 civilians in Iraq, Afghanistan, Pakistan and elsewhere “died violent deaths as a direct result of the war on terror,” according to Brown University researchers’ Costs of War project. The total number of people killed — civilians plus U.S. and allied troops, enemy fighters, contractors, journalists, and aid workers — approaches one million. Close to 40 million humans have been displaced by the ravages of war, and the cost from the destruction of buildings and infrastructure is incalculable. This road to this misery and mayhem was paved with good intentions: after al-Qaeda struck the U.S., the Bush administration, with the assent of Congress and other key American institutions, launched the Global War on Terror with the aim of eliminating terrorists and ending tyranny, as President Bush proclaimed in his second inaugural address in January 2005. In this episode, Brown University anthropologist Catherine Lutz and Southern Methodist University presidential historian Jeffrey Engel discuss how and why U.S. foreign policy took such a disastrous turn.