9/11 and Iraq has no direct connection from what I know.
Now that doesn't mean we should have not gone into Iraq, but 9/11 was not caused by Iraq.
Iraq, unlike any nation in the world, even North Korea and Iran, has totally disobeyed about 16 security council orders after the first war in Iraq was supposed to make them honor them. I don’t think their is any country in the world that lost a war and totally disregarded the peace treaty.
In a post 9/11 world, that can not be allowed to continue. Not to mention the WMD's they claimed to have all the time, we had to go in a see for ourselves.
RANT
The only relation to 9/11 and Iraq is that in a post 9/11 world we can not allow countries like Iraq to be so against world order and civility.
If we are to call Iraq a supporter of terrorism then we can also call Saudi Arabia a terrorist supporter as well... but we seemingly need to do business with Saudi Arabia soooo... the are OK.
And you wonder why the Muslim pop. is so railed against he US? Since the 60's it was used as a pawn in a super power cold war battle, regimes supported were also very bad to their own people (including Saddam Hussein remember?), and Israel does actually get away with stuff they should not get away with on a consistent basis even though it is as simple as not to expand anymore (the claim of 'for safety' doesn't work when you have people living on the claimed lands).
Not to worry cause the US knows what is best. The USSR would have been far worst than the Saudi regime or Hussein. They should thank us.
END RANT
So in the end, post 9/11 is not directly related to Iraq or Iran, nor North Korea and other places BUT clearly we can not allow Cold War alliances and mistakes to mean that these places can continue doing what they do without consequences.