The spectacular advances by ISIS forces in Iraq in recent days have been a catastrophe for Iraq and a major setback for American interests but they are not the end of the world.
ISIS (the Islamic State of Iraq and Syria) now holds substantial swathes of territory and may have something like $2 billion in cash, a fleet of armored vehicles and probably more small arms than it knows what to do with. Unusually among jihadist groups, ISIS has focused in Syria on governance beyond just shooting, beheading, and crucifying people it doesn’t like. Presumably it will do the same in Iraq.
However, this will not last. For an explanation why, we can turn to probably the most brilliant jihadist strategist to have touched a keyboard: Abu Musab al-Suri. He believed that “open fronts,” such as the 1980s jihad against the Soviet Union, efforts intended to liberate and hold territory, are unlikely to succeed. The simple fact is that they cannot stand up to modern military power backed up by modern intelligence. Instead, he recommended a turn toward individual jihad because it avoided the enemies’ strengths. In other words, Al-Suri would say that the more cities ISIS captures, the more money it has to keep track of, the more armored vehicles it acquires, the more social services it has to organize and deliver, the more it is setting itself up for a fall. These things have all sorts of pernicious effects from the point of view of security: they tie ISIS to fixed territory, they create networks that can be mapped and exploited, and they provide targets to airpower and artillery. ...I'm not sure that ISIS will pass or, even if it does, that things will return to normal.
ISIS has passed the point of merely being a guerrilla movement. It now holds a large enough contiguous territory to be considered a nation-state, with sufficient forces to challenge Iraq's military on equal terms. It has accepted the reigns of government, providing infrastructure and social services generally provided by governments. It has--at least for now--a generally supportive population. The Iraqi government has proven itself incapable of stopping ISIS's advances, and will probably be equally unable to retake substantial territory, unless (as in the surge during the American occupation) ISIS alienates the population. In short, ISIS is at the same point Mao was in China when the tide turned against the Nationalist Chinese.
Even if ISIS is pushed back, though, its actions are a watershed event for Iraq. The Kurds will demand greater independence from Iraq's central government and get it. I suspect that now that they have control of Kirkuk, the Kurds are not going to cede it back. The Kurds are strongly positioned to declare an independent state, which will, more likely than not, lead to armed conflict with Turkey.
Even if ISIS is defeated, it will not end the Sunni/Shiite split in Iraq. The Sunni's will have had a taste of the power they lost upon the U.S. invasion, and will want it back--at least to the extent of having their own autonomous region.
Finally, if ISIS is defeated militarily, they will merely melt back to the stage 1 of revolution, becoming fish in a sea of Sunni supporters.