Uhh, they are there because of the inhumane treatment the people were receiving from their devil leader.
We are still there because there is no true form of an operating government yet.
If we left them now, it would only be a matter of months before another dictator rose from among the warring tribes.
Whether the US is there or not...hate to break it to you but the warring would continue.
It was going on long before we got there, and will continue if we don't stay until a stabalized form of government can rule.