And then their people suddenly got tired of modernity and tried to crawl back into the past.

On the left, technological optimists were replaced by Rousseauian romantic primitivists. In the 1970s, Green guru Amory Lovins promulgated the gospel that “hard” sources of energy like nuclear power are bad and that called for a “soft path” based on hydropower, wind and solar energy. Other Green romantics decided that even hydropower is wicked, because it is generated by dams that despoil the prehuman landscape.

The New Left of the 1960s and 1970s longed for small, participatory communities, and rejected the giant organizations that New Deal liberals had taken pride in. In the 1980s and 1990s, new urbanists converted most progressives to their nostalgia for the ephemeral rail-and-trolley based towns of the late nineteenth century. GM foods, which New Deal liberals like Franklin Roosevelt and Lyndon Johnson would have embraced as a way to feed multitudes while sparing land for wilderness, were denounced by progressives who favored “heirloom” turkey and melons that the Pilgrims might have eaten. The increasingly reactionary American left, disenchanted with nuclear power plants and rockets and suburbs, longed to quit modernity and retire to a small town with an organic farmers’ market and an oompah band playing in the town park’s bandstand.

A similar intellectual regression to infantilism took place on the right in the late twentieth century. Between the 1930s and the 1970s, conservatism was defined by big business anti-statism, not by neotraditionalism. The Republican opponents of New Deal Democrats shared the New Dealers’ faith in science, technology and large-scale industry. They just wanted business to keep more of its prerogatives.

Contrast Eisenhower-era business conservatism with the religious right of Pat Robertson, Jerry Falwell and other evangelicals and fundamentalists in the late 20th and early 21st centuries. By 2000, an entire national party, the Republicans, was intimidated by religious zealots. No Republican presidential candidate could support legal abortion or criticize the pseudoscientific “creationist” alternative to evolutionary biology. Hatred of biotechnology, in the form of GM foods and human genetic engineering, was shared by the regressives of the left and the right. First a Democratic president, Jimmy Carter, then a Republican, George W. Bush, sought votes by claiming he had been “born again” with the help of Jesus, something that no president before the 1970s would have claimed.

Today optimism about science and technology is found chiefly on the libertarian right. At least somebody still defends nuclear energy and biotechnology. But in libertarian thought, science and technology are divorced from their modernist counterparts — large-scale public and private organizations — and wedded to ideals of small producers and unregulated markets that were obsolete by the middle of the nineteenth century. Libertarian thought is half-modern, at best. To its credit, it does not share the longing of many on the left for the Shire of Frodo the Hobbit or the nostalgia of most of the contemporary right for the Little House on the Prairie.

If there was a moment when the culture of enlightened modernity in the United States gave way to the sickly culture of romantic primitivism, it was when the movie “Star Wars” premiered in 1977. A child of the 1960s, I had grown up with the optimistic vision symbolized by “Star Trek,” according to which planets, as they developed technologically and politically, graduated to membership in the United Federation of Planets, a sort of galactic League of Nations or UN. When I first watched “Star Wars,” I was deeply shocked. The representatives of the advanced, scientific, galaxy-spanning organization were now the bad guys, and the heroes were positively medieval — hereditary princes and princesses, wizards and ape-men. Aristocracy and tribalism were superior to bureaucracy. Technology was bad. Magic was good.

The Dark Age that began in the 1970s continues. Today’s conservatives, centrists, progressives — most look like regressives, by the standards of mid-20th century America. Tea Party conservatives argue that federal prohibitions on child labor are unconstitutional, that the Fourteenth Amendment should be repealed, and that the Confederates were right about states, rights. Religious conservatives, having lost some of their political power, continue to their fight against Darwinism. Fiscally conservative “centrists” in Washington share an obsession with balanced budgets that would have seemed irrational and primitive not only to Keynes but also to the 19th-century British founder of The Economist, Walter Bagehot. And while there is a dwindling remnant of modernity-minded New Deal social democrats, most of the energy on the left is found on the nostalgic farmers’market/ train-and-trolley wing of the white upper middle class.

Here’s an idea. America needs to have a neomodernist party to oppose the reigning primitivists of the right, left and center. Let everyone who opposes abortion, wants to ban GM foods and nuclear energy, hates cars and trucks and planes and loves trains and trolleys, seeks to ban suburbia, despises consumerism, and/or thinks Darwin was a fraud join the Regressive Party. Those of us who believe that the real, if exaggerated, dangers of technology, big government, big business and big labor are outweighed by their benefits can join the Modernist Party. While the Regressives secede from reality and try to build their premodern utopias on their reservations, the Modernists can resume the work of building a secular, technological, prosperous, and relatively egalitarian civilization, after a half-century detour into a Dark Age.