Cultural impact of the September 11 attacks
The cultural impact of the September 11 attacks (9/11) was profound and extended well beyond geopolitics, spilling into society and culture in general. Many Americans began to identify a "pre-9/11" world and a "post-9/11" world as a way of viewing modern history.
Source: Wikipedia — Cultural impact of the September 11 attacks (CC BY-SA 4.0)