It’s time to ponder a troubling possibility: What should we do if the Islamic State wins? By “wins,” I don’t mean it spreads like wildfire throughout the Muslim world, eventually establishing a caliphate from Baghdad to Rabat and beyond. That’s what its leaders say they are going to do, but revolutionary ambitions are not reality and that possibility is particularly far-fetched. Rather, an Islamic State victory would mean that the group retained power in the areas it now controls and successfully defied outside efforts to “degrade and destroy” it. So the question is: What do we do if the Islamic State becomes a real state and demonstrates real staying power?

That possibility is looking more likely these days, given Baghdad’s inability to mount a successful counteroffensive. If MIT’s Barry Posen is correct (and he usually is), the Iraqi Army no longer exists as a meaningful fighting force. Not only does this reveal the bankruptcy of the U.S. effort to train Iraqi forces (and the collective failure of all the commanders who led this effort and kept offering upbeat assessments of progress), but it also means that only a large-scale foreign intervention is likely to roll back and ultimately eliminate the Islamic State. This will not happen unless a coalition of Arab states agrees to commit thousands of their own troops to the battle, because the United States will not and should not do the fighting for states whose stake in the outcome exceeds its own.

Don’t get me wrong — I’d be as pleased as anyone if the Islamic State were decisively defeated and its violent message utterly discredited. But one needs to plan not just for what one would like to see happen, but also for the very real possibility that we can’t actually achieve what we want — or at least not at a cost that we consider acceptable.

So what do we do if the Islamic State succeeds in holding on to its territory and becoming a real state? Posen says that the United States (as well as others) should deal with the Islamic State the same way it has dealt with other revolutionary state-building movements: with a policy of containment. I agree.

Despite its bloodthirsty and gruesome tactics, the Islamic State is not, in fact, a powerful global actor. Its message attracts recruits among marginalized youth in other countries, but attracting perhaps 25,000 ill-trained followers from a global population of more than 7 billion is not that significant. It may even be a net gain if these people leave their countries of origin and then get to experience the harsh realities of jihadi rule. Some of them will realize that the Islamic State is brutal and unjust and a recipe for disaster; the rest will be isolated and contained in one spot instead of stirring up trouble at home.

More importantly, the relative handful of foreigners flocking to fight under the Islamic State’s banner are only a tiny fraction of the world’s Muslims, and the fanatical jihadi message shows little sign of winning significant support in this large and diverse population.

I’m not being naive. Islamic State fellow travelers will no doubt conduct terrorist acts and cause other forms of trouble in various places. But that is a far cry from the Islamic State’s being able to spread willy-nilly across the Islamic world. The group clearly has the potential to cause trouble outside the stretch of desert that it currently controls, but it hasn’t yet demonstrated a significant capacity to expand beyond the alienated Sunni populations of western Iraq and eastern Syria.

Moreover, the Islamic State’s territory has few resources and little industrial power. Its military forces, though capably led, are not those of a great power (or even a regional power). The Islamic State faces strong resistance whenever it tries to move outside Sunni areas (e.g., into Kurdistan or Shiite-dominated Baghdad), where it cannot exploit local resentment against Baghdad or Damascus.

The Islamic State faces another important obstacle: It no longer enjoys the advantage of surprise. It emerged unexpectedly from the chaos of post-invasion Iraq and the Syrian civil war, and it featured the unlikely marriageof an extremist strand of Islam and some prominent former Baathist officials who knew how to run a police state. The combination has been surprisingly effective, just as the Iraqi Army has been (unsurprisingly) corrupt and unreliable. But the Islamic State’s potential to cause trouble is now clear, and Arab states, from the Persian Gulf to Egypt and beyond, will now go to considerable lengths to make sure the Islamic State model does not take root in their own societies. (Libya is another matter, after the foolhardy Western intervention there, but the emergence of an Islamic State clone there is also a containable problem.)

Now take an imaginative leap. Assume the Islamic State is contained but not overthrown and that it eventually creates durable governing institutions. As befits a group built in part on the former Baathist thugocracy, it is already creating the administrative structures of statehood: levying taxes, monitoring its borders, building armed forces, co-opting local groups, etc. Some of its neighbors are tacitly acknowledging this reality by turning a blind eye to the smuggling that keeps the Islamic State in business. Should this continue, how long will it be before other countries begin to recognize the “Islamic State” as a legitimate government?

This might sound preposterous, but remember that the international community has often tried to ostracize revolutionary movements, only to grudgingly recognize them once their staying power was proven.

This might sound preposterous, but remember that the international community has often tried to ostracize revolutionary movements, only to grudgingly recognize them once their staying power was proven. The Western powers refused to recognize the Soviet Union for some years after the 1917 Bolshevik revolution, and the United States did not do so until 1933. Similarly, the United States did not establish full diplomatic relations with the government of the world’s most populous country — the People’s Republic of China — until 1979, a full 30 years after the PRC was founded. Given these (and other) precedents, can we be certain that the Islamic State might not one day become a legitimate member of the international community, with a seat at the United Nations?Perhaps, you’ll say, the Islamic State’s barbaric behavior — enslaving women, torturing civilians, beheading hostages — will forever exclude it from the community of civilized nations. Isn’t it more likely that its leaders will end up in the dock at the International Criminal Court than addressing the U.N. General Assembly? It would be nice to think so, but history suggests a more cynical lesson.

Those oh-so-posh and civilized Brits we enjoy watching on Downton Abbey? Their ancestors created the United Kingdom through violent and brutal acts of coercion and conquest (as any knowledgeable Welshman or Scot could tell you). Those heroic Americans who expanded the “Empire of Liberty” across North America? They massacred, raped, and starved Native Americans to get there — and collected plenty of scalps along the way. The Bolsheviks and Maoists who created the USSR and People’s Republic of China? They didn’t consolidate power via gentle persuasion, and neither did the Wahhabis under Ibn Saud or the Zionists who founded Israel. As the now-deceased Charles Tilly made abundantly clear in his landmark Coercion, Capital, and European States, state-building has been a brutal enterprise for centuries, and the movements that built new states in the past did many things that we would now condemn as utterly barbaric. (And let’s not pretend that today’s “advanced” societies are uniformly genteel or moral either. An innocent blown up by an ill-aimed drone strike is just as much a victim as someone brutally beheaded by the Islamic State.)

The norms of “acceptable” state conduct have changed dramatically over the past century, which is why we rightly regard the Islamic State’s behavior as especially abhorrent today. Pointing out that other state-builders acted badly in the past neither excuses nor justifies what the jihadis are doing today in Iraq and Syria. But this long history does remind us that movements that were once beyond the pale sometimes end up accepted and legitimized, if they manage to hang onto power long enough.

To be accepted into the community of nations, however, radical or revolutionary movements eventually have to abandon some (if not all) of their most ferocious practices. As Kenneth Waltz pointed out more than 30 years ago, eventually all radical states become “socialized into the system.” Over time, they learn that their grandiose ideological ambitions are not going to be realized and that uncompromising fidelity to their original revolutionary aims is costly, counterproductive, and maybe even threatening to their long-term survival. Within the movement, voices arise that call for compromise, or at least a more pragmatic approach to the outside world. Instead of “world revolution,” it becomes time to build “socialism in one country.” Instead of spreading the “Islamic Republic,” it becomes time to cut deals with both Great and Lesser Satans. The new state gradually adapts to prevailing international norms and practices, and it eventually moves from pariah to partner, especially when its interests start to coincide with those of other states. It may still be a troublesome presence in world politics, but it is no longer ostracized. If the Islamic State survives and consolidates, that is what I’d expect to happen to it as well.

But make no mistake: This process of “socialization” does not happen automatically. Radical states don’t learn that beastly behavior is costly unless other states join forces to impose the necessary penalties. If the Islamic State manages to cling to power, consolidate its position, and create a genuine de facto state in what was previously part of Iraq and Syria, then other states will need to work together to teach it the facts of life in the international system. And because the Islamic State is not in fact that powerful, preventing it from expanding or increasing its power and imposing costs for its abhorrent behavior should not be all that hard.

The chief task for American statecraft, therefore, should be to coordinate and back up an international campaign of containment in which local actors such as Saudi Arabia, Jordan, Turkey, and Iran — which have the most at stake — take the lead role. It also means helping others counter the Islamic State’s efforts to spread its message, convincing other states to do more to limit its sources of revenue, and patiently waiting for its excesses to undermine it from within.