People flee their homes during fighting between Iraqi and Islamic State forces during a military operation to regain control of Hit, 85 miles west of Baghdad. (Khalid Mohammed/Associated Press)

David Petraeus, the chairman of the KKR Global Institute, is a retired U.S. Army general who commanded coalition forces in Iraq from 2007 to 2008 and Afghanistan from 2010 to 2011 and served as CIA director from 2011 to 2012.

The formulation of sound national policy requires finding the right overarching concepts. Getting the “big ideas” right is particularly important when major developments appear to have invalidated the concepts upon which previous policy and strategy were based — which now appears to be the case in the wake of the Arab Spring.

To illustrate this point, I have often noted that the surge that mattered most in Iraq was not the surge of forces. It was the surge of ideas, which guided the strategy that ultimately reduced violence in the country so substantially.

The biggest of the big ideas that guided the Iraq surge included recognition that:

●The decisive terrain was the human terrain — and that securing the people had to be our foremost task. Without progress on that, nothing else would be possible.

●We could secure the people only by living with them, locating our forces in their neighborhoods, rather than consolidating on big bases, as we had been doing the year before the surge.

●We could not kill or capture our way out of the sizable insurgency that plagued Iraq; rather, though killing and capturing were necessary, we needed to reconcile with as many of the insurgent rank and file as was possible.

●We could not clear areas of insurgents and then leave them after handing control off to Iraqi security forces; rather, we had to clear and hold, transitioning to Iraqis only when we achieved a situation that they could sustain.

Now, nine tough years later, five big ideas seem to be crystallizing as the lessons we should be taking from developments over the past decade.

First, it is increasingly apparent that ungoverned spaces in a region stretching from West Africa through the Middle East and into Central Asia will be exploited by Islamic extremists who want to establish sanctuaries in which they can enforce their extremist version of Islam and from which they can conduct terrorist attacks.

Second, it is also apparent that the attacks and other activities of such extremists will not be confined to the areas or regions in which they are located. Rather, as in the case of Syria, the actions of the extremist groups are likely to spew instability, extremism, violence and refugees far beyond their immediate surroundings, posing increasingly difficult challenges for our partners in the region, our European allies and even our homeland.

Third, it is also increasingly clear that, in responding to these challenges, U.S. leadership is imperative. If the United States does not lead, it is unlikely that another country will. Moreover, at this point, no group of other countries can collectively approach U.S. capabilities. This does not mean that the United States needs to undertake enormous efforts to counter extremist groups in each case. To the contrary, the United States should do only what is absolutely necessary, and we should do so with as many partners as possible. Churchill was right when he observed, “There is only one thing worse than fighting with allies, and that is fighting without them.” And, if one of those partners wants to walk point — such as France in Mali — we should support it, while recognizing that we still may have to contribute substantially.

Partners from the Islamic world are of particular importance. Indeed, they have huge incentives to be involved, as the ongoing struggles are generally not clashes between civilizations. Rather, what we are seeing is more accurately a clash within a civilization, that of the Islamic world. And no leaders have more to lose should extremism gather momentum than those of predominantly Islamic states.

Fourth, it is becoming clear that the path the United States and coalition partners pursue has to be comprehensive and not just a narrow counter-terrorism approach. It is increasingly apparent that more than precision strikes and special operations raids are needed. This does not mean that the United States has to provide the conventional ground forces, conduct the political reconciliation component or undertake the nation-building tasks necessary in such cases. In Iraq at present, for example, it is clear that the Iraqis not only should provide those components, but also that they have to do so for the results achieved — with considerable help from the U.S.-led coalition — to be sustainable.

Fifth, and finally, it is clear that the U.S.-led effort will have to be sustained for what may be extended periods of time — and that reductions in our level of effort should be guided by conditions on the ground rather than fixed timetables. While aspirational timelines for reductions in our efforts may have some merit, it is clear from our experiences under both post-9/11 administrations that premature transitions and drawdowns can result in loss of the progress for which we sacrificed greatly — and may result in having to return to a country to avoid a setback to U.S. interests.

To be sure, there is nothing easy about what I describe. Success in all such efforts will require sustained commitment, not just of our military forces, but also of the capabilities of other departments and agencies.

A comprehensive approach is neither easy nor cheap. But that is also true of the actions we have to take as inadequately governed spaces become ungoverned and in turn are exploited by transnational extremists.

The Long War is going to be an ultramarathon, and it is time we recognized that. But we and our partners have the ability to respond in a thoughtful, prudent manner, informed by the big ideas that I have described. Nothing less will prove adequate.