FAREED ZAKARIA WRITES, correctly, that Iraq’s problems are fundamentally political not military: “The reality is that only an effective political bargain will bring about order. There needs to be a deal that gives all three communities strong incentives to cooperate rather than be spoilers.”
The Iraqi Oil Trust idea, originally proposed here via Lou Dolinar (and see the followup posts here, here, and here for more) might be one way to accomplish this.