It's a dormant empire. Remember the empire did not collapse by itself even though it was pretty weak. Western nations helped to finish it off and then set up puppet states with puppet rulers to ensure it doesn't come back quickly. The Islamic Empire is simply built on Muslims joining in unison for common interests and against common enemies. It's like no other empire before, it's not based on race or region but on belief, a belief system which is not just very much alive but growing. It's just a matter of time before this empire is awake again from it's slumber. The more the western nations attack Islam and Muslims the quicker it's revival is coming about.
There are many reasons why they set up 911 and conducted one of the biggest deceptions in the history of mankind but the main reason was to give them leverage to protect the Zionist state and to go to war with for the Zionist state. It's obviously made life easier for Israel to continue stealing land and there is no way multiple attacks on nations including Pakistan, Afghanistan, Iraq, Libya, Somalia could take place without the excuse of 911.