Why demolishing WTC?(Noob here)

Hi everybody.I remember the day when the 9/11 happened,i was at my aunt's home and i saw the news and the planes crashing.I was 11,12 back then,so i didn't quite realized what was going on.As years passed by,i started to be curious about this event.I've read a lot of theories and conspiracies about it,and i just saw a video and read lots of stuff about the bombs that were rigged on the WTC and various accounts of multiple explosions and strange devices.
I agree there's something weird in this event,but,why bringing down WTC?why throwing a missile against the pentagon?
I'm 17,i know next to nothing about politics and such,i'm not even american,so i'd like to hear some replies from more 'enlightned' users.I'm not looking for the real truth,i'm almost sure that won't be ever known,i'm looking for opinions and facts,so i can construct my own.

Thanks in advance

Slightly similar thread posted here recently:
www.abovetopsecret.com...

You would probably be better off reading a 9/11 timeline on wikipedia or similar site. And then look at theories that some have presented.

The event was a catalizing moment in the worlds history. Buildings collapsing on emergency responders and others left an imprint on everyone who gave a damn about your fellow human beings. That being said, the responce was predictable, I know I wanted revenge! We were told in the following days just who it was and ofcoarse we (well most of us) believed! Now years later it still hasn't been explained to my satisfaction, nor alot of other peoples. So here we are sifting through the wreckage so to speak looking for the truth.