The transformation in American strategic thinking that took place after 9/11 amounted to a judgment by some that the nexus of failed, repressive and rogue states, on the one hand, and globalization, transnational terrorism, radical Islamic ideology and easier accessibility to WMD, on the other, posed an existential threat to international security and global development. We know that the ambitions of al-Qaeda are limitless; we do not know exactly what al-Qaeda’s capabilities are or might be. The worst-case scenario is dire: nuclear bombs in Los Angeles, London, Berlin and Tokyo.

Would such an event bring an end to the United States, the United Kingdom, Germany or Japan? No. But it would transform the way in which these states organized their societies, depress global economic growth, and put an end to the conventional rules of sovereignty that have, for better and worse, guided international politics for the few centuries. What might such an “end” lead to? Ungoverned spaces would be occupied. The global financial system, which transfers of billions of dollars daily, would be more tightly controlled to prevent the funding of radical Islamist activities. The Middle East oil fields would be seized by more powerful states, or perhaps declared to be part of the common heritage of mankind with revenues contributed to international financial institutions. This would be a much messier and more dangerous world.

There is no way to confidently assign probabilities to this scenario, or to one less horrific but still likely to catalyze significant political regression, such as the use of dirty nuclear bombs or multiple attacks with chemical or biological agents. But stranger things than mega-terrorist attacks have happened in the last century. The rise and collapse of the Soviet Union, Nazi control of Germany, two world wars and the Holocaust, the tens of millions killed by the policies of Stalin and Mao, and the rapid democratization of central Europe under the tutelage of the European Union were all bizarre and improbable events.

In the face of the prospect of radical upheaval, Barry Posen argues that the appropriate way to address the challenges facing the United States is through a policy of restraint that would scale back alliances, use force more reticently, and be more modest about the possibilities for political transformation within and among countries. I am skeptical.

The benefits of scaling back alliances, the clearest implications of Posen’s conception of strategic restraint, are outweighed by the risks. A more modest NATO might inspire greater security commitments from Europe, but it might not. A weaker U.S. position in Asia might lead Japan to engage its neighbors, or it might aggravate the security dilemma and precipitate an arms race. The United States could be more pointed with regard to Israeli occupation policies, but distancing itself from Israel would signal a lack of American support that would make major war more likely, not less.

The harder issues for the United States are not the future of its alliances but the appropriate use of military force, and the extent to which the United States, with its allies, can change domestic authority structures in other countries. External actors can promote political change, including even transformations to liberal democracy. Central Europe’s movement from communism to liberal democracy, a transformation that could not have taken place without the incentives, procedures and promise offered by the European Union, is the most successful example of democracy promotion even seen. American military intervention in the Caribbean and Central America in the 1980s and 1990s did contribute to more open and accountable regimes in several countries, if not ideal liberal democratic ones. And, of course, there are always the examples of Japan and Germany.

It is hard to promote movement toward liberal democracy, however, and there have been many failures as well as some successes. Organizational forms are relatively easy to transfer, but the substance and culture of institutions are not. Every liberal democracy has followed its own trajectory, and even the United States, perhaps the most successful political regime in history, has had a very bumpy ride that has included a civil war.

Supporting freedom, openness and democracy is like a venture capital investment. Information is imperfect. Contingencies matter. Leadership can be crucial. We know in general that incentives are better than bribes, that domestic allies are essential, that past experience with democracy helps, that it is better to be richer than poorer, that military force can sometimes precipitate lasting change. But we do not know with certainty what devices or combinations of devices will bring success in a particular place.

Given the threat posed by the nexus of failed and repressive states, globalization, and the diffusion of military power to non-state as well as state actors, is restraint really the optimal U.S. strategy? Leaving aside the ambiguity of what restraint means, let me offer another slogan: opportunism or, better yet, flexibility.

The United States and other liberal democracies need an array of instruments to promote movement toward more open, liberal and accountable regimes. They also need, of course, conventional intelligence sharing and policing to combat domestic as well as transnational terrorist threats. Policy cannot just be about elections and democracy in some narrow sense. It must also involve, as Posen recognizes, the protection of human rights, the promotion of civil society, support for more open media and the rule of law. Economic openness offers powerful incentives. Trade agreements are not just about trade; they involve changing domestic institutions in partner countries in ways that can enhance American security.

I make no claim for opportunism or flexibility as a grand strategy. Like restraint, these terms are little more than slogans. They do not have the kind of heuristic power needed for framing a genuine grand strategy. It is not from any lack of effort that six years after 9/11 we still have no consensus about grand strategy. An effective grand strategy must be based on a shared conception of the nature of the challenge, and that is something we lack. Restraint is a strategy for those who believe that U.S. activism itself is the problem, not for those who believe otherwise.