Is a United Iraq Necessary?

Yesterday Farid Zakharia interviewed General Mc Chrystal on his show, Global GPS. Essentially the general said that defeating ISIS will involve not just a military victory but also winning over the population. That is no small order. The original Iraq war started by the Bush Republican administration gummed up the situation by exposing the limitations of US power and breaking up the humpty dumpty Iraq which we are now trying to put back together. If ISIS could be replaced by a secular Sunni country in Wetern Iraq and possibly eastern Syria along tribal lines without the barbarism of ISIS, friendly to the USA, Israel, Kurdistan, and the West, that would not set well with the Shiite government in Bagdad but they have had more than a decade to get their act in order. It would not set well with Iran. It would set well with the Sunni countries like Saudi Arabia and Egypt. Perhaps just the threat of it might make the central Iraqi government more central rather than just Shiite. Every solution seems to create new problems. Which of the bad solutions is the least bad? Is a united Iraq necessary?