Final answer:
Al-Qaeda was responsible for the September 11, 2001 World Trade Center attacks in New York City.
Step-by-step explanation:
The terrorist group responsible for the September 11, 2001 World Trade Center attacks in New York City was Al-Qaeda. Al-Qaeda is an international terrorist network that claims to be waging a holy war against the West and the United States. On that day, nineteen terrorists who were affiliated with al-Qaeda seized control of four commercial airliners and crashed two of them into the Twin Towers, causing their collapse.