What were the cause of the 9/11 attacks?
user
The attacks were caused by al-Qaeda, an Islamist militant group.  They hijacked several airplanes and flew them into the World Trade Center and the Pentagon.
assistant
What were the cause of the 9/11 attacks?
user
The attacks on 9/11 were carried out by terrorists who took over four commercial passenger jet aircraft and used them as bombs.
assistant
What were the cause of the 9/11 attacks?