Thomas Friedman has a truly frightening column in today's NY Times. He writes about how Iraq is so close to the tipping point:

The fate of the entire U.S. enterprise in Iraq now hangs in the balance, as the war has entered a dangerous new phase. It is the phase of barbaric identity-card violence between Sunnis and Shiites. In the late 1970's, I covered a similar moment in Lebanon, and the one thing I learned was this: Once this kind of venom gets unleashed — with members of each community literally beheading each other on the basis of their religious identities — it poisons everything. You enter a realm that is beyond politics, a realm where fear and revenge dominate everyone's thinking — and that is where Iraq is heading.
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Once embedded, this cycle of fear and revenge is almost impossible to break. People conclude that the only thing that can protect them is a militia from their own sect, not the police or the army. Then these militias, which come to life to protect the neighborhood, take on a life of their own. They develop protection rackets, feel the thrill of power and, as that happens, start to do all they can to prevent the government from restoring its authority. Finally, as the BBC noted in a recent report from Baghdad, some Iraqi politicians are now concluding that "they can gain more power and influence from building on sectarian loyalties than from appeals for national unity." When politicians decide they can get ahead by appealing more to fear than to hope, national reconciliation goes up in smoke.

A Baghdad blogger, the Mesopotamian, quoted by AndrewSullivan.com...."I don't know anymore what can be done to rescue the situation. At least, those who are supposed to be in positions of responsibility should stop lying and painting a false picture. ... I regret sounding so pessimistic, but the alarm must be sounded. ... What is happening is Baghdad is something really awful."
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The Iraqi Shiite community showed remarkable restraint in the face of the murderous provocations by these Islamo-nihilist gangs during the past three years. But that restraint is over. It's now clear that some Shiite militias are ready to match the Sunni nihilists, killing for killing. So the slide into a medieval barbarism has begun.

Do not believe any of the Bush team's happy talk. It doesn't matter if Iraq is quiet in the south and quiet in the north. If Baghdad, the heart of the country, is being ripped apart, then there is no Iraq — because there is no center.

Friedman is right. In the next few months, look for the insurgent violence to escalate mainly in and around Baghdad. As goes that key central city, so goes the entire country -- and the militias know this fact full well. While Iraq may be fairly large geographically, when it comes to obtaining power the acknowledged reality is only a small part of the country needs to be conquered.