The first is the dispute over Kirkuk, capital of At-Tamim province. The city and its environs contain some 10 billion of Iraq’s 112 billion barrels in proven oil reserves. Saddam Hussein expelled thousands of Kurds as well as Turkomans and Christians from the Kirkuk region in the 1980s and 1990s, replacing them with Arabs, mainly Shia from the south, themselves victims of his repression. With Saddam gone, roughly 350,000 Kurds moved back (some original residents, others not) with active support from the Kurdistan Regional Government (KRG). Thousands of Arabs fled, alleging threats and attacks by Kurdish groups. The influx also displaced Turkomans, but they continue to stake their own claim to Kirkuk, supported by Turkey.

Iraq’s Constitution requires a referendum on Kirkuk’s future status by the end of this year, and as the deadline nears, the carnage increases. Car bombs, sectarian murders (fanned by Al Qaeda in Mesopotamia), and expulsions abound. The vote will make matters worse. The run-up will almost certainly be marred by violence, and Arabs and Turkomans will reject a Kurdish victory. But the Kurds threaten to leave Iraq’s government if it is postponed, as the Iraq Study Group recommended. Kirkuk looks like the Gordian knot that can’t be cut.

The second problem involves Mosul, Iraq’s third largest city and capital of Nineveh province, which lies just west of Iraqi Kurdistan. Sunni militias and Al Qaeda have been targeting Mosul’s Kurds, who are fleeing to Kurdistan or areas near its border. Kurdish militias have retaliated, but have not been drawn into a full-blown civil war. That could change, which is what Al Qaeda wants; a new front would further stretch American forces.

Nineveh’s tensions also stem from the underrepresentation of Sunnis, who boycotted the 2005 provincial elections. Some observers recommend fresh elections to redress the imbalance, but absent a minimum of trust, the elixir of elections won’t work and could make things worse. The Kurds constitute a third of Mosul province’s population but now hold three quarters of the seats in its council and also control most key administration positions; they won’t part with political power to placate the Sunnis.

The third problem is the redoubts established in Iraqi Kurdistan by the Kurdistan Workers’ Party (PKK), the militant separatist organization from Turkey’s Kurdish southeast. Turkey has periodically launched artillery and air strikes, covert operations and cross-border incursions against suspected PKK positions in northern Iraq. In recent weeks top Turkish generals and politicians have taken a hard line, warning of new incursions if the KRG does not take steps to expel the PKK. Ankara upped the ante this month by massing troops and armor on its border with Iraq, and though it denied the reports of a cross-border move by thousands of its troops on June 6, the tensions are clearly rising.

But the KRG won’t cave and evict the PKK. The Iraqi Kurds and their leaders are generally sympathetic to Turkish Kurds. In response to Turkish threats, the two top Iraq Kurdish leaders (Iraq’s President Jalal Talabani and KRG president Massoud Barzani) have countered that the KRG could retaliate by supporting Turkey’s restive Kurds.

U.S. Defense Secretary Robert Gates recently urged Turkey to stay out of northern Iraq, but can Washington stay Ankara’s hand? Only if the Kirkuk dispute is settled in a manner that does not hand the territory to the Kurds, the KRG checks the PKK, and Iraq holds together. One would be foolish to bet a large sum on any of these scenarios.

Moreover, the Iraq War has spawned strong anti-American nationalism in Turkey. Opinion polls show that a majority of Turks believe that Washington, a longtime ally, now seeks to truncate Turkey, presumably by allowing an independent Iraqi Kurdish state to emerge on its southern flank. This animosity has reduced any leverage Washington has on Turkish leaders.

With the surge having mixed results at best and Americans’ patience with the war eroding, the one place in Iraq where the Bush administration could show evidence of success seems headed for trouble. If northern Iraq descends into chaos, President Bush’s vow to stay the course will become even less credible—not just to Americans, but also to Iraqi insurgents and Al Qaeda.