The many anti-globalist politicians, parties, and movements roiling the politics of Western liberal democracies can be understood in many ways. But the most fruitful may be to view them as the latest representatives of an old tradition of opposition to the 18th-century Enlightenment and its legacy to our world.

The Enlightenment legacy can be seen all around us: individualism, international commerce and trade, moral cosmopolitanism, freedom of the press and a culture of publicity, technological modernity, the valorization of expertise, and on and on.

Back in the 1760s, when these and many other norms and ideals were just beginning to emerge in Europe, a series of writers began to question their worth — and to claim that a society based upon them would be disastrous for human happiness and flourishing. But now, for the first time in many decades, their descendants are gaining traction in debates, winning votes in elections, and rising to positions of political power. Those of us on the Enlightenment's side in the dispute owe it to ourselves to become acquainted with the most cogent and compelling claims made by the leading opponents of our position. That is the only way to defeat them.

The Enlightenment began as an act of rebellion against complacency. Demoralized by what they saw as centuries of intellectual and economic stagnation, as well as decades of pointless religious civil wars, the leading figures of the Enlightenment (Locke, Montesquieu, and Kant, among many others) advocated a series of reforms. Europeans needed to learn to think for themselves, founding a culture of criticism, applying healthy doses of skepticism to the claims of political and ecclesiastic authorities, and bringing rational criticism to bear on received institutions and customs. They needed to advocate the use of the scientific method to increase the sum total of human knowledge and apply these findings to the betterment of human life through technological advances. They needed to spread this knowledge among the common people to enable a greater degree of self-government. They needed to encourage and reward international commerce and trade, both to raise standards of living and diminish the likelihood of conflict between states.

This was the agenda of the Enlightenment, which lives on to this day in the norms, practices, and beliefs that prevail among intellectual, cultural, economic, political, and journalistic elites throughout the Western world.

But the agenda has been dogged by critics from the beginning — and not just ecclesiastical and political critics who rose up in defense of their own privileges against the reformers. Far more formidable were the philosophical critics, who had no stake in defending the old order for its own sake. Instead, these critics worried that a world transformed in precisely the ways advocated by the Enlightenment would be a world marked by psychic and spiritual misery along with new forms of economic oppression and conflict.

The first and possibly greatest of these critics was Jean-Jacques Rousseau, who became notorious in the 1760s and '70s for claiming that a highly educated, civilized, and "enlightened" world would be filled with profoundly alienated and unhappy people who felt deeply divided against themselves, longing for a lost sense of wholeness and fulfillment that remained forever beyond their grasp. This unhappiness, Rousseau predicted, would give birth to tyrannical political movements and unprecedented forms of moral degradation (which to some extent he exemplified in his own life).

Building on Rousseau's insights and prophecies, Johann Gottfried Herder argued in the 1770s and '80s that the cosmopolitan Enlightenment project would lead to social and psychological fragmentation. Human beings are naturally social, Herder claimed, and they depend on and thrive most fully within linguistic-cultural wholes that form a unified context of meaning and purpose. Without that intact context, individuals feel lost, alone, bereft, miserable. The way to combat these maladies is the self-conscious construction of a new political whole of the "nation." (Herder was Europe's first theorist of and advocate for nationalism.)

This first wave of counter-Enlightenment thought crested and dissipated around the turn of the 19th century. Over the next several decades, as Europe modernized, underwent industrialization, endured a series of wars, and experienced numerous revolutions, reform movements, and successful efforts at national unification, the legacies of the Enlightenment and its critics left their marks from one end of the continent to the other.

Only in the closing decades of the 19th century did the critiques of Rousseau and Herder come surging back in a new and far more radical form. Writing in the 1870s and '80s, Friedrich Nietzsche described a modern world in which all forms of greatness had been flattened out into universal mediocrity and nihilism. The causes of this decline were complex, but one aspect of it was the Enlightenment's ill-advised and naïve "will to truth" — its foolish disregard for humanity's equal and opposite "will to ignorance." Push people to live in the glaring light of truth and they will end up blinded, prone to lunging for relief toward the opposite extreme of complete darkness.

Martin Heidegger developed this insight further during the 1920s and '30s, writing about how the founders of civilizations and peoples wrest collective meaning from the nothingness that underlies human existence in all of its forms and that threatens to overwhelm and engulf all such meaning in the modern, enlightened world. For a time, Heidegger became a devoted Nazi because he believed Adolf Hitler was doing precisely this — overcoming modern meaninglessness by leading the German people on a quest to forge a new way of being-in-the-world that appropriated and transformed the German past and projected it onto a grand, indeterminate future.

In his later thought, after his extravagant hopes for National Socialism had been dashed, Heidegger came to view the modern world as an undifferentiated, irredeemable "wasteland" thoroughly permeated by technological modes of thinking, acting, and living. For the late Heidegger, the only hope for redemption from absolute nihilism involved the deconstruction of technological modes of thought and then the expectant waiting for the revelation of a new god who might make possible the advent of "another beginning" — beyond modernity, beyond mass politics, beyond the Enlightenment and its pernicious legacy.

If such eschatological pronouncements sounded portentous when Heidegger uttered them (in the 1950s and '60s), they came to seem bizarrely anachronistic once the Cold War drew to a close and many in the West began to entertain the possibility that history had culminated in a world universally destined for enlightenment liberalism.

But the "end of history" lasted barely more than a decade. Buffeted by a series of shocks over the past 16 years — the 9/11 attacks, the Iraq War, the financial meltdown, the dashed hopes of the Arab Spring, the Syrian civil war, the rise of ISIS, and the refugee crisis in the European Union — the liberal order bequeathed by the Enlightenment looks more vulnerable today than it has at any time since the 1930s. That mood of pessimism is both a cause and an effect of the resurgence in counter-Enlightenment thinking in our time.

Among Heidegger's most influential admirers today is Aleksandr Dugin, the Russian fascist philosopher who serves as Vladimir Putin's informal ideological guru. One of Dugin's books, Martin Heidegger: The Philosophy of Another Beginning, has been translated into English by Nina Kouprianova, who just so happens to be the ex-wife of alt-right white supremacist Richard Spencer.

The point of rehearsing this history isn't to bring the counter-Enlightenment tradition up on the charge of thought-crime, or to engage in an act of guilt by (Nazi) association. The point is, rather, the opposite: to emphasize how vitally important it is for those who wish to defend the Enlightenment and its legacy — along with its vision of human life, both individually and collectively — to engage deeply and thoughtfully with its most challenging, resourceful, and resilient critics. The fact that these ideas have come roaring back so forcefully after so many years in eclipse is a powerful indication that they can't be dismissed as glibly as some of the Enlightenment's side of the debate would like.