I don't know, starting a war on the other side of the planet is a pretty big radius.

Maybe it was not a defining moment for the world at large, but it was a defining moment for the US.

It broke the 90s economy. It created a lot of doubt in the US stock market about future terrorist attacks, causing an immediate run to pull out money, and starting a very quick, sudden recession.

As an immediate aftermath, all US airlines had to pause operation. When flights resumed, airlines had to find a way to make lost revenue, kicking off rapid enshitification. Though most airlines did not collapse, they hit hard times, further feeding into the collapsing market.

Prior to the attacks, the US was in a relatively peaceful period. In response to the attacks, the US started yet another war against the Middle East and has been at war with one country or another for almost 25 years.

It also justified the government to create a giant system to monitor people worldwide. The government set up secret courts to try Americans. People outside the country, were simply kidnapped and detained in Guantanamo Bay.

Now, many of these things are simply cyclic progressions or had been brewing long before September 2001, but the event creates a very clear border between before and after.