The September 11 attacks serve as a critical historical lens through which to view the trajectory of American power in the 21st century. Following the attacks, the United States initiated significant shifts in foreign policy, military engagement, and domestic security, which many analysts argue have fundamentally altered the nation's global standing.

Some observers contend that the long-term costs of the subsequent 'War on Terror'—both financial and in terms of international reputation—have contributed to a gradual decline in American hegemony. This perspective suggests that the focus on interventionist policies diverted resources and attention from domestic challenges, potentially weakening the country's internal stability and global appeal. Conversely, other analysts argue that the post-9/11 era demonstrated the resilience of American institutions and the capacity of the nation to adapt to unprecedented security threats.

There is disagreement regarding the extent to which this 'waning' is a direct result of post-9/11 policies versus broader geopolitical trends, such as the rise of other global powers. While some sources emphasize the erosion of soft power and the strain on democratic norms as primary factors, others focus on the necessity of the security measures taken at the time. The discourse remains divided between those who view the post-9/11 period as a strategic overreach that accelerated a decline, and those who see it as a necessary, albeit difficult, chapter in maintaining national security in a changing world.