Well, the political reason behind the war in Iraq is Sadam's involvement with Al Qaeda terrorist groups. The second reason, which was recently proven to be false, was that Sadam has access to BioChemical weapons. This poses a threat to the US given the radical behaviors of Sadam and his ties to Al Qaeda.
You said it is a "small region," but I beg to differ. The middle east is small compared to the US, but definitely much more populated. Also, you might also want to consider that alot of the people in the regions support the acts of Al Qaeda forces; therefore, making it harder for us to find Osama.
As far a the conspiracy, I dont think there was one. I however do think Bush is extremely...monkey stupid. The war in Iraq was a poor call, based on unverified intelligence. The war did however succeed in giving Bush a nice political push to his reelection, detering all attention from his other failed policies. That's most likely the true reason why this war was initiated, but I'm not against stripping bio weapons from the hands of a war tyrant either.