9/11 is the embodiment of revenge. It took a 9/11 for us to realize the importance of forgiveness and to stop stooping to another's act of violence for that is an endless loop. stoop=loop. Insanity is doing the same thing over and over and expecting a different result.
In order for history to stop repeating itself a change must take place at the core of one's being.

The outside world is the inside world writ large. The universe reflects your heart.
Prior to 9/11 revenge was a larger part of the human condition. Since the individual now keeps himself more in check and is more conscious of his actions with love being the basis for it, in part because of events like 9/11 and [his]tory being sharp reminders and time being the keeper of such aspects of the self.
Forgive and forget:

Strength will be your greatest ally in your quest to not lose the now / present / gift.