The terrorist group responsible for the attacks in New York was Al Qaeda.
Al Qaeda is a paramilitary organization that employs terrorist practices and poses as an islamist resistance movement around the world, while it is commonly referred to as an internacional terrorist network.
The attacks of september 11, 2001 were a series of four terrorist attacks committed on the morning of tuesday september 11, 2001, by 19 members of Al Qaeda, by stealing commercial aircraft to be hit against various targets, causing a lot of damage as well as the destruction in New York of the entire building complex of the World Trade Center.
This episode would generate the war against Afghanistan and the adoption of the US Goverment and its allies in the so called 'war against terrorism' policy.