9/11 has become such a polarizing event in history, that much like in politics or religion, it often requires to parse one's words carefully before engaging it. Two conflicting narratives are at play; and both have ample evidence to back them up depending on who you speak with. The official version of the events is that foreign nationals planned and executed a painstakingly crafted terrorist attack on the U.S under the auspices of Osama Bin laden, the leader and founder of the militant organization al-Qaeda.
The alternative version, a rather engrossing narrative of a dastardly act allegedly perpetrated, or at the very least tacitly allowed by the U.S. to take place, is the preferred narrative of the "9/11 Truthers," or "9/11 skeptics," a vocal group of independent conspiracy theorists who ardently dispute the findings of the 9/11 Commission Report and instead try to pin the 9/11 event on a nefarious group of global power players, whose sole purpose in life is to create chaos in order to further their shadowy agenda.
No matter which side of the story you find yourself supporting, it is quite clear that 9/11 was pivotal in changing America forever and not necessarily for the better. Freedoms were curtailed, the U.S was plunged into a never-ending war against 'terror' that has generated anti-American sentiments in a large portion of the world, and the nation became a Petri dish for all kinds of outlandish and ugly ideologies cultivated and trafficked online not only by social-media-age agitators, but even by our very own elected officials.