Besides oil, I think the main reason why is to establish a powerhouse of a country that would serve as a counter-balance to Iran. America would have greatly benefitted from a strong, stable, friendly, (and oil rich) country in a region that doesn't like us too much. Remember, America is not an altruistic country. We do nothing unless it will benefit us. I could think of at least 30 countries off the top of my head that could use our help. But alas, if you were to analize it as a business, our Return on Investment would be low. As for Iraq, our leadership greatly miscalculated and we are paying the price in blood, treasury, and reputation.