It was a terrible day for America, and that was the motive.
Osama bin Laden (when he was alive if he is even dead) said why repeatedly that the attacks would have continue until specific foreign policies (American policy in the Middle East and its support of Israel) are stopped. I think the motive was to get American presence out of the Middle East.
The fight between Muslims and Christians has been going on for over a thousand years back to 'The First Crusade' and it will likely continue for another thousand.
If by "there" you mean the ppl who engineered 9-11, it was simply GREED. The rich and powerful just want more and more and, just like Pearl Harbor, are willing to sacrifice anyone to get it!
the united states motive was never ending wars in the middle east.it was an inside job.
terrorism