Answer:
Prior to the attacks of September 11, 2001, the Al Qaeda organization and its leader Osama Bin Laden were already known as an extremely dangerous terrorist organization.
Already in 1998, with the attacks on the American embassies in Kenya and Tanzania, and in 2000 with the attack on the American ship USS Cole, Al Qaeda had proved to be an anti-American and anti-Western terrorist organization. As of 2001, with the attacks on the World Trade Center, the threat of Al Qaeda caused an international response, which was called War on Terror.