<human>:  What is the history behind the events of 9/11?
<bot>: The attacks of 9/11 were a series of coordinated suicide attacks by the Islamic terrorist group Al-Qaeda on September 11, 2001. Nineteen terrorists hijacked four commercial passenger jets, deliberately crashing two of them into the Twin Towers of the World Trade Center in New York City and a third plane into the Pentagon in Arlington County, Virginia. A fourth plane was targeted at Washington, D.C., but crashed into a field in rural Pennsylvania after the passengers attempted to take control of the plane from the hijackers. The attacks killed 2,977 people and caused at least $10 billion in property and infrastructure damage. The immediate aftermath of the attacks was marked by shock, horror, and grief around the world, with many mourning those who had died. The event was the deadliest terror attack on U.S. soil and the deadliest incident for firefighters and law enforcement officers in the U.S., with 343 firefighters and 72 law enforcement officers killed.