When terrorism succeeds – and fails

US difficulties in Iraq and the "surge" of American forces into Baghdad raise again the important question: When does terrorism succeed or fail? Neither Robert Gates, the new secretary of Defense, nor the Iraq Study Group have provided an answer.

Many conclude that terrorism almost invariably succeeds. But this response does not distinguish between two different situations. Among established governments, provincial terrorism designed to divide the mother country into separate parts has largely failed. National self-determination foisted by terrorists is coming to an end. But terrorism directed against foreign intervention has frequently succeeded – and may continue to do so.

The record of terrorist failures is long and instructive. Despite inflicting terror on Russia and Ingushetia, Chechen insurgents have not won independence from Russia. Though threatened by terrorism, the central governments of Britain, Indonesia, and India have not conceded to terrorists in their midst. The solutions in Northern Ireland, Aceh, and Kashmir have been successful combinations of force and cooperation.

Governments have reasserted control through inducement and military opposition. Around the world, interior ministries cooperate to gain intelligence against terrorists.

The IRA in Northern Ireland has abandoned terror tactics. Radical Basques still support ETA and its terror campaign, but most of Spain rejects it. Canada has not heeded the demands of some Quebeckers for independence, and the Parti Quebecois bears no resemblance to the old and discredited actions of the FLQ. Sri Lanka is not likely to break apart, and most Sri Lankans don't support the extremist tactics of the separatist Tamil Tigers.

In each case, dissidents have undermined their legitimacy by resorting to mass killings, extortion, and suicide bombings. In the Middle East, Palestinians are discrediting themselves as fitting citizens of a new national unit.

In this respect, terrorism has definitively failed. But countries that intervene into the domestic affairs of other states confront a different and more successful form of terrorism or insurgency. That's because intervention most often destroys the very government and political class that occupiers need as a rebuilding partner. Successful military interventions require overwhelming force, large troop concentrations, strong multinational support – and the quick reestablishment of central government.

Having written a manual on the subject, the new US command in Iraq, Gen. David Petraeus, knows full well what he faces in Baghdad. The "surge" will not be effective unless the US can bring the Sunnis into what has been largely a sectarian Shiite regime, partly controlled by insurgent militias. It may be tempting to give Sunnis a central province in Anbar and Baghdad, with Shiites and Kurds running their own areas elsewhere. But that would be a mistake.

Aside from the problem of how to share oil revenues, evidence suggests that breaking Iraq up into Shiite, Sunni, and Kurdish compounds may ultimately occur as a result of civil war, but the US should not sponsor it. Studies of terrorism suggest that the key variable leading to success is getting an effective central government that controls sticks and carrots to sway the insurgents to come in from the cold. For this, the US needs a different and stronger Iraqi regime, not beholden to one camp. It may be too late to get this, but without an effective and broadened government, the US effort in Iraq will fail.

The US previously acted upon this theory when it went into Afghanistan in 2001. The "loya jirga" meeting in Bonn fashioned a balanced regime in Kabul that most of the country accepted. That structure has helped the country make important strides in recent years. But because US resources have been overwhelmingly spent in Iraq, the Afghan government has few carrots or sticks. Afghanistan still faces major security challenges, and greater military and economic assistance must play a part in overcoming them. But unlike in Iraq, the US, NATO, and the Afghans themselves have created an inclusive political environment that encourages violent extremists to become political stakeholders. Whatever happens in Iraq, the US, its allies, and the Afghan people can still unite Afghanistan and make its government reflect the desires of the nation.

• Richard Rosecrance, an adjunct professor at Harvard's Kennedy School of Government, is the co-editor of the book "No More States? Globalization, National Self-Determination, and Terrorism." The views here are his own.