What Biden outlined was pointedly not an end to the post-9/11 era. Rather, it was a much narrower admission that an idea once shared by conservatives, liberals and foreign policy elites, including Biden himself — that the U.S. could use force to destroy other societies and then rebuild them in America‘s image — had proved a failure. And it was an acknowledgment that the nature of warfare, not the enemy, has changed for the world‘s pre-eminent superpower.