EDITOR’S NOTE: This is the final installment of a three-part series.

The new barbarian threat, like that of old, grows out of civilizational backwardness. Specifically, the Islamist radicals who now plot against us are a product of the political, economic, and cultural failures of the underdeveloped world. Brooding resentment of those failures has mixed with fundamentalist Islam to produce a totalitarian ideology bent on an apocalyptic showdown with the West.

Outside the West’s golden circle of trust live five billion of the earth’s six billion people. In the underdeveloped world, it is the underdevelopment of institutions that is especially debilitating. In a continuum from bad to worse — from corrupt officials and inadequate courts, to laws so dysfunctional that many or most people are chased into the underground economy, to the arbitrary confiscations of kleptocratic misrule, to the chaos of Hobbesian anarchy — the poorer countries are all plagued by the insufficient formal protection of property and contract rights. And exacerbating (and at least partially explaining) that formal institutional breakdown are traditional cultural mores in which no moral obligations are owed to people outside some small and insular “in-group,” whether it be family or village or tribe or sect. In this institutional setting, exchanges between strangers are more or less limited to face-to-face, on-the-spot transactions where little trust is necessary. The large-scale, long-term investments that are needed to create Western-style affluence are few and far between.

Institutional backwardness has been compounded by the collectivist delusion that swept through the underdeveloped world during the postcolonial era. Collectivism sought an end-run around high transaction costs. Rather than reducing them by creating conditions in which ordinary people could trust each other and do business together, the various ideologies of state-dominated economic development pinned their hopes on top-down control by a state-backed elite. The result was a debacle. State ownership and control of industry did produce large-scale investments that aped Western economic structures, but by and large they were sinks of monopoly and corruption rather than fonts of dynamism and growth. Meanwhile, centralized control over economic life went hand in hand with the concentration of political power, and dictatorship of one or another stripe became the norm in poorer countries. Collectivism, far from transcending the need for broad-based trust, served only to exacerbate its victims’ backwardness.

In recent decades many poorer countries have turned away from the old statist nostrums and begun to embrace more market-oriented models of economic development. Most of the Muslim world, however, remains a dilapidated mess. Egypt, Syria, and Iraq still groan under unreconstructed Arab socialism. In Iran, Reza Pahlavi’s despotic “White Revolution” was replaced by the worse despotism of the mullahs. Pakistan is a dismal wreckage of tribal enmities held together by corruption and brutality. And Saudi Arabia suffers through the late seasons of Beverly Hillbillies’s economics. Whatever the local variations, tyranny and stagnation are the common themes.

The Muslim world is by no means unique in its general failure to build vital, dynamic, high-trust societies. Dysfunctional institutions are depressingly commonplace throughout sub-Saharan Africa, Latin America, and Asia. What is distinctive about the Muslim world today is its combination of failed modernization and a culturally potent ideology that is profoundly hostile toward Western modernity — namely, the ideology of fundamentalist Islam. With the hopes raised by collectivism and oil wealth dashed, a rabidly intolerant strain of Islam has surged in to fill the vacuum. Amidst the prevailing disillusionment and despair, its message, in effect, is: “If you can’t join ‘em, beat ‘em.” It offers the fantasy that the House of Islam can be restored to its former glory through radical rejection of the values of the culture that eclipsed it. That fantasy inspires the mad terrorist jihad with which we now contend.

The terrorists’ strategy is, of course, delusional to the point of psychosis. No faith, however blind, will make rote memorization of ancient texts, suppression of critical inquiry and dissent, subjugation of women, and servile deference to authority the recipe for anything other than civilizational decline. The Islamists therefore cannot win, at least not as they conceive victory. All they can do is try to bring us down to their level. But on that score, the threat they pose is formidable.

In the longer view, the threat of the new barbarism goes far beyond Islamist totalitarianism. Over time, the chaos of underdevelopment could spawn other radical anti-Western movements. Less speculatively, there are fringe political movements here in the West — white supremacists on the right, radical environmentalists and animal-rights zealots on the left — that have already demonstrated their willingness to use violence against their fellow citizens. Likewise, apocalyptic cults can double as terrorist cells, as happened with Aum Shinrikyo in Japan. Although members of such groups may have been born and raised among us, their deep alienation from the larger social order can make them, in effect, internal barbarians — enemies of a civilization that, psychologically at least, they are unable or unwilling to make their home.

Today, however, the barbarians of totalitarian Islamism are the clear and present danger. To carry the fight against them, we must proceed on many fronts. First, and most obviously, we must go after the terrorist organizations themselves. We must pursue, relentlessly, the leadership and foot soldiers of al Qaeda and company — kill them or capture them when we can, harass them, deny them safe haven, dry up their sources of funding. This campaign began in Afghanistan, and continues in shadowy global operations today. The great danger here is complacency. Unlike in conventional wars with their shifting battle lines, there will be little clear feedback by which to gauge our progress. Accordingly, there will be an ever-present temptation to slacken resolve and fool ourselves that all is well — until the moment when catastrophe strikes.

In addition, we must make every effort to keep weapons of mass destruction out of terrorist hands. Here attention has focused, understandably, on confronting rogue states like Iraq, Iran, and North Korea. And, indeed, such states must be disarmed — no ifs, ands, or buts. At the same time, however, we must dedicate ourselves to the less glamorous but vitally important task of safeguarding and ultimately destroying the massive Soviet-era stockpiles of nuclear and biological materials. Unfortunately, there are worrying signs that this latter task is not being approached with proper seriousness. In particular, the United States continues to support a harebrained joint project with Russia to convert weapons-grade plutonium into nuclear fuel — despite the fact that this project will greatly increase the opportunities for theft of this extraordinarily dangerous material.

Improving domestic security is likewise essential. Between the Keystone Kop routines of airport security and the hemming and hawing over a new Cabinet agency, suffice it to say that we can do much, much better — and must do better if today’s political leaders hope to avoid the haunting reproaches of tomorrow’s innocent dead.

The ultimate demise of the steppe nomads came when their geographical base was eliminated — that is, when the vast grasslands that sustained them were finally put under the plow. In the same way, we must work to deprive our terrorist adversaries of their natural habitats. In particular, the political and economic repression that is so sadly commonplace in Muslim countries is a breeding ground for Islamist extremism, and thus a direct threat to the security of the United States. Over the coming years and decades, therefore, U.S. policy should support the rollback of chaos and misrule and the advance of liberal democracy throughout the region.

When conflict is unavoidable, as with Afghanistan and Iraq, that policy will rely on the force of American arms. Otherwise, we must use all the diplomatic resources at our disposal — including more determined efforts to integrate the region into the larger global economy; an end to subsidies (whether through bilateral foreign aid or the IMF and World Bank) that prop up despotic regimes; the exertion of pressure, both public and private, on repressive regimes to allow dissent and political competition and respect the rule of law; and the encouragement of liberal movements within the region.

Finally, we must carry the battle to the realm of ideas. The slouching relativism and decadent ennui that rationalize appeasement must be kept at bay; more than that, they must be scorned and ridiculed and stigmatized. This is not to say that there must be unanimity about all matters concerning the war — not at all. But there can be no acceptable dissent regarding the West’s moral superiority to Islamist totalitarianism, or the right of liberal civilization to defend itself effectively against the barbarian threat. Simply put, there can be no tolerance of intolerance.

In the 20th century, the open society of liberal modernity faced and surmounted a great internal challenge. Totalitarians of the left and right sought to substitute top-down control for bottom-up trust as society’s central organizing principle; they did so in a mad quest to replace open-ended dynamism and growth with static, utopian perfection. Now in the 21st century, that internal rebellion has been put down, but utopian delusions continue to crop up in the periphery — in the broken lands of the underdeveloped world, and the broken souls of fringe groups in the West. These new rebels have no realistic prospect of gaining power over the society they hate, but they can inflict damage upon it — grievous damage. This is the enemy we face today: utopians turned nihilist, totalitarians turned barbarian.

The first step in countering this latest threat is understanding its true nature and dimensions. As always, keeping our freedom requires unceasing vigilance.