The great ideas of the nineteenth century changed as well. One might even state without too much hyperbole, the great ideas not only changed, but they devolved. More than anything else, the greats of the western tradition of the nineteenth century narrowed the thoughts of those who had come before them. Whereas Jefferson, Edmund Burke, and Adam Smith—the great greats of the eighteenth century—began with the beginning, the nature of nature, the nature of natural law, and the nature of rights, the greats of the nineteenth century narrowed, narrowed, narrowed, and then exploded one truth to insanity, allowing it to overpower all other truths. With Karl Marx, everything was economic. With Charles Darwin, everything was biological. With Sigmund Freud, everything was psychological. True enough, the human being is, of course, economic, biological, and psychological. Yet, the human person is so much more than this, almost infinitely complex and various. Jefferson, Burke, and Smith not only fought systematic thoughts, men of system, and what would be called ideologies, but they also each contented themselves with the beginnings of the human person, not the ends of the human person. In other words, in contrast to their nineteenth-century inheritors, these eighteenth-century thinkers found the minimum equality necessary for a dignified life, allowing the individual person and community to make its own way through trial and error, success and failure, charity and failing.
Because the greats of the nineteenth century—each to his own varying degree—accepted one truth at the expense of all others and relied, entirely, on materialist explanations of the world, they fundamentally failed to understand the nature of the human person, the nature of existence, and the nature of history. This is not to deny their individual and particular brilliances, but rather only to note that by ignoring the spiritual element of humanity, they offer nothing that can be seen as successful in the long run of society. From Heraclitus forward, the greats of the western tradition have sought to understand both the material and spiritual elements of existence, recognizing the overwhelming complexities not only of life, but also of each individual life.
As such, history will, most likely, understand the nineteenth century as a failure in human thought, but it will also recognize that even the failures had successes, especially rather grand if temporary ones. To be sure, it would be nearly impossible (and utterly foolish) to dismiss the influence that Marx, Darwin, and Freud had on those who came after them.
— Read on theimaginativeconservative.org/2019/03/nietzsche-short-nineteenth-century-bradley-birzer.html