Six years have now passed since the Islamist terrorists turned airliners into cruise missiles to attack the World Trade Center buildings in New York and the Pentagon in Arlington. In the intervening years, we have launched major military operations against the Taliban/al Qaeda in Afghanistan, and against Saddam Hussein’s regime in Iraq. A combination of U.S. technology, U.S. Special Operations Forces, and indigenous forces routed the Taliban in 2001-2002. U.S. forces swept into Baghdad in the spring of 2003, ending Saddam’s reign. But the war goes on. The Taliban has reconstituted itself in the tribal regions of Afghanistan along the Pakistani border, while the war in Iraq quickly morphed into an insurgency. Intelligence reports indicate that al Qaeda has also reconstituted, in spite of the death and capture of many of its operatives.

At the same time, paradoxically, complacency has set in among the American public. As Mark Steyn asked Sunday on National Review Online, if there’s no terror, how can there be a war on terrorism? The government’s very success in preventing a repeat of 9/11 has led some to conclude that the threat has been oversold. In academia, things are worse. A growing number of professors of international relations and political science have concluded that al Qaeda is an artifact created by the U.S. government to justify emergency measures. My own institution, the Naval War College, is not immune to such views.

But complacency aside, the world is different now. For one thing, the character of terrorism has changed which makes it difficult to return to the days when terrorism was a threat best addressed by law enforcement.

The change was anticipated by Walter Laqueur in his 1999 book The New Terrorism: Fanaticism and the Arms of Mass Destruction, which is an expanded version of his earlier essay "Postmodern Terrorism," that appeared in the September/October 1996 issue of Foreign Affairs. The thesis of both the article and the book is as follows: increased access to weapons of mass destruction combined with the apocalyptic vision of many terrorist groups meant that today’s terrorism—and the likely terrorism of the future—differs qualitatively from that which had gone before.

Terrorism has a long history, but in the past, the ability of terrorists to wreak havoc was limited by their own political goals and the weapons available to them. Now the proliferation and easy availability of destructive technologies make it possible for even small, marginal groups to have an impact far out of proportion to their numbers. Two years before 9/11, Laqueur observed that as horrifying as the Oklahoma City bombing, the first World Trade Center attack, and the bombing of U.S. embassies in Africa may have been, they would be dwarfed by a terrorist attack using weapons of mass destruction—chemical, biological, or radiological.

With some clear exceptions, most terrorists over the past century have espoused nationalist or left-wing ideologies. But Laqueur argued that terrorism was becoming increasingly a phenomenon of religious fanaticism. He argued that the conditions that foster religious fanaticism are likely to remain features of both developed and developing nations for the foreseeable future.

Laqueur argued that state-sponsored terrorism had not disappeared, but that its impact was likely to remain limited because sponsoring states wish to limit their exposure to retaliation. Not so for the "exotic" terrorists, such as al Qaeda, who fervently embrace ruthless violence to achieve their goals. The growing importance of fanaticism and paranoia in modern terrorism; the replacement of the use of violence as a means of achieving ideological ends, with the use of violence as an end in itself; and the potential capability of terrorist groups to wreak unprecedented destruction by means of weapons of mass destruction, all make terrorism far more dangerous than it once was.

This leads to the obvious question: what constitutes "victory" against such an adversary? As my friend and former Naval War College colleague, Bill Martel, now a professor at the Fletcher School, points out in his recent book, Victory in War, "we do not have a framework for victory beyond the implicit assumption that the unalloyed purpose of strategy is to achieve it."

"There is no theory or precise language of victory that permits policymakers, military officials, and the public to agree on what ’victory’ means or when ’victory’ has been attained." This is clear today as we execute a war against Islamist terrorism in general and against al Qaeda in Iraq in particular.

Defeating the enemy can constitute a victory, but only if military success is translated into political success. After all, wars are not fought for their own sake but to achieve a favorable peace. The reason defeating the enemy is not sufficient in itself for victory was articulated by Clausewitz: "In war, the result is never final… The defeated state often considers the outcome merely as a transitory evil, for which a remedy may still be found in political conditions at some later date."

The successful translation of an enemy’s defeat into true victory is rare in history. World War II is one example. But even surrender does not necessarily lead to victory. Although Confederate armies surrendered at Appomattox and Durham Station, much of the social system of the militarily-defeated south was successfully reestablished in the years following the Civil War. The war is over when the loser, not the winner, says it is.

What would constitute victory in the war against the network of Islamist terrorists? The only meaningful metric is what Martel calls grand-strategic victory, the "strategic successes that occur through the destruction of a society, its military, economy, and institutions of government." I would add to this list the defeat of the ideology that underpins Islamist terrorism. One of the reasons for the collapse of the Soviet Union and the end of the Cold War was that Communist ideology was successfully discredited.

As was the case with communism during the Cold War, the ideology of radical Islamist terrorism cannot be defeated by military might alone. Military success in Iraq, Afghanistan, and elsewhere can buy us time. But in the long run, grand strategic victory against the network of Islamist terrorists requires defeat of their murderous ideas. The problem here is that many in the West are beginning to reject the principles of liberalism, and just when adherence to those principles is most necessary to achieve victory in a war of ideas.

Mackubin T. Owens is an Adjunct Fellow of the Ashbrook Center and an associate dean of academics and a professor of national-security affairs at the Naval War College in Newport, R.I. He is writing a history of U.S. civil-military relations.