The USA screwed up in funding the mujahideen in Afghanistan, which included Bin Laden, against the Russian invasion, which in turn led to 9/11, which in turn led to a USA invasion of Afghanistan instead.
Some rather tenuous assertions of cause-and-effect we have here.
OBL was a self-propelled force. There's no indication that the US supported him, or even knew about him until 1996. To suggest that the US operation in Afghanistan up through 1989 (make of it what you will) "led to 9/11" seems quite specious indeed.
The guy listed many grievances in his justification for the 9/11 attacks, but (AFAIK) the prior US support for the Muj (i.e. the very people he was fighting with), or any aspect of it doesn't seem to have been one of them. Rather, it was all that stuff about the Holy Sites, US presence in the gulf (on behalf of regimes he didn't like), and last but not least the fact of Clinton going after him directly (and trying to kill him in fact) which seem to have lit his flame.
(And then the idea of 9/11 "leading to" the Afghanistan invasion is a wholy different, and even more convoluted thread -- but which also seems to have been sufficiently addressed by others already).
