9 years, and America still feels the impact of this very event. How could it be forgotten? To those who don't believe it affected the world, they couldn't be more wrong. It started a war. For those who love peace, they mourn 9/11 because it shattered the peace of the world. Wars were started, economies were affected, and relations between countries strained as America seeks to bring the terrorists to justice.
But not just what I described above happened. Muslims ended up with egg on their faces, even the honest Muslims who would do nothing to harm a fly ended up taking the blame from the bigoted people. Their extremists had done a horrible thing, so I think every sane Muslim in the world would mourn on this day, because they were horrified at what was done. I know that their scripture calls people to fight for their faith, but I'm certain that most of their non-extremist religious leaders felt that America was not any threat to the faith at all, even a year before the attacks.
The world was affected indirectly in many ways. Even people in the UK were affected in the years that follow, there were terrorist attacks in England, just to name one of many countries affected.