MUST READ

"The argument that we should keep troops in Iraq to balance Iran never resonated with Iraqis, most of whom do not wish to be drawn into a conflict between the United States and Iran.  Nor was it clear that a small residual force would have deterred Iran.  It may well have had the opposite effect: fueling recruitment to Iranian-backed extremist groups."

"Consequently, our trying to force an agreement through the Iraqi parliament would have been self-destructive. That had nothing to do with Iran and everything to do with Iraqi pride, history and nationalism. Even the most staunchly anti-Iranian Iraqi officials refused to publicly back a residual U.S. force — and in the end, they supported our withdrawal."

http://www.washingtonpost.com/opinions/not-an-end-but-a-beginning-in-iraq/2011/11/03/gIQA1jBqjM_story.html

According to Lawrence J. Korb writing in American Progress --

"There was never any credible evidence that Iraq possessed nuclear weapons or had ties to Al Qaeda. In fact, Al Qaeda did not come into Iraq until after we began our occupation. By the time we invaded in 2003, Saddam Hussein was contained and growing weaker by the day, and neither NATO nor the U.N. thought our actions were legally or morally justified. Invading Iraq 18 months after September 11th made as much sense as invading fascist Spain after the attacks on Pearl Harbor."

http://www.americanprogress.org/issues/2009/08/afghanistan_strategy.html