Some people do say these things, but they are making empty debaters’ points. They ignore the intrinsic claims of nationalism and religion and the circumstances of human existence that give rise to them. The circumstances that gave rise to today’s nationalist awakening, at least in the West, have nothing to do with suppressing minorities or invading foreign lands. Instead, the new nationalism is a revolt against the failures and weaknesses of modern nation-states. It is neither intolerant nor triumphalist but rather is defensive, grounded in well-justified apprehensions of political and institutional decline.

In America, the nationalist claim is that the federal government has abdicated basic responsibilities and broken trust with large numbers of citizens:

• It has failed to secure the national borders and provide regular procedures for immigration and assimilation.

• It has delegated lawmaking to foreign and international bodies, and domestic bureaucracies, that have scant regard for the interests and values of many of our fellow citizens.

• It has acquiesced in, or actively promoted, the splintering of the nation into contending racial, religious and other groups and has favored some at the expense of others.

• It has neglected core American principles and traditions—separation of powers, due process, the presumption of innocence, local prerogative, freedom of association—allowing them to atrophy or be subjected to political conditions.

These claims are closely aligned with traditional conservative precepts, although conservative politicians and activists have not always adhered to them in recent decades. That is why the nationalist awakening is a conservative awakening, too, and presents distinct opportunities for those of our persuasion.

Which brings me to the second parallel with the Great Awakenings. Adamant revivalist energies, while unruly and disruptive, may be precursors to social enlargement and a new sense of collective purpose. I am choosing my words carefully and did not say “national unity” and “cohesion”—that has never been the American Way, outside wars and similar crises, and it never could be. All we need is a serviceable consensus on the essentials of American identity and character, sufficiently broad and representative for the tasks of cultural and political reform.

The national conservatism we are developing is going to have some hard edges and provoke some clever counterattacks and dismissals. The rancor proves the seriousness of the challenge we face. As the Danish physicist-poet Piet Hein wrote: “Problems worthy of attack / Prove their worth by fighting back.”

But the American nation is not only vast, heterogeneous and fractious but also tough, resilient and practical. The ideas conservative nationalists are developing have broad transcultural potential. Modern progressivism has turned against essential precepts of the American liberal tradition, such as equal opportunity and freedom of inquiry, religion and enterprise. We are assimilating them into conservatism, and old-fashioned liberals cannot help but notice.

An important virtue of the nation-state is that it is a constraint. The contemporary peaceable nation takes what it is given—its borders and territory and resources, its citizens and tribes, its affinities and antagonisms, its history and traditions and ways of getting along—and makes the most of them. The order of independent nation-states addresses international problems by working with the positions and interests of individual nations as they are. Many idealists would prefer to avoid these constraints by operating through stateless, single-minded political structures.

One of the most arresting features of modern life in the rich democracies is the pervasive rejection of the idea of natural constraint. One sees this throughout culture high and low, social relations, and politics and government. Where a boundary exists, it is there to be transgressed. Where a hardship exists, it must be because of an injustice, which we can remedy if only we have the will. Today’s recipe for success and happiness is not to manage within limits and accommodate constraints, but to keep one’s options open. The newest frontier is the notion that even your sex is an option, and the sooner young children are informed of this, the better.

I do not know where this impulse came from. Perhaps wealth and technology have relieved so many age-old constraints that we have come to imagine we can live with no constraint at all. Whatever the cause, it is a revolt against reality. Resources are limited. Lasting achievement is possible only within a structure. My own favorite field, economics, is out of favor these days, but it has at least one profound truth, that of opportunity cost: Everything we do necessarily involves not doing something else.

The illusion of unlimited optionality has been especially damaging in government and politics. A dramatic recent instance came in the Democrats’ presidential primary debates, where many candidates favored both open borders and free health care for everyone who shows up. This would plainly amount to the abolition of the United States. Still, the proponents would say in all earnestness that they have ingenious plans to make it work.

That is an extreme instance of the phenomenon that every social problem or inconvenience summons forth costly new spending or regulatory solutions, with hardly a care to where the resources will come from or what other problems will be slighted. It is a bipartisan phenomenon, and it has left us with a massively indebted government that spends trillions of borrowed dollars on our immediate needs, with the bills kited to future generations.

The American nation-state is rich, powerful and less constrained than any other, yet it is much more constrained than we have led ourselves to believe. Thinking of ourselves as a nation-state is, as Peter Thiel has observed, a means of unromantic self-knowledge. National conservatism, by directing our attention to our nation as it is—warts, wonders and all—is a means of reminding ourselves of our dependence on one another in the here and now, and of facing up to the constraints that are the sources of productive freedom.

Mr. DeMuth is a distinguished fellow at the Hudson Institute. This is adapted from a speech he delivered at the National Conservatism Conference.