9/11 led to Obama being elected ... so there's that. I digress, why would I want to change anything that happened in the world? If you prevented 9/11 who's to say that another attack wouldn't have happened that was on the same level or even worse? What if D-Day had been stopped? Or had the Holocaust never occurred and WW2 never taken form? Then the United Nations, European Union, and NATO would cease to exist quite possibly. Chances are the Great Depression would have lasted a lot longer, we would have never crippled the infrastructure of Europe and Japan, leading us to never being a power horse in the Automotive and labor industry. Every bad thing that happens in history leads to something good.