In 1941, a few months before the United States entered World War II, magazine publisher Henry Luce called on Americans to establish "the first great American century". America, he argued, had become the world's most powerful nation but refused to act like it. Luce believed America had to commit itself to promoting democratic internationalism. In the years that followed, as the US helped found the United Nations, joined security alliances like NATO and ANZUS, and pushed for free trade agreements across the globe, Luce's dream was largely realised.

The year 2016 may well mark the end of the American century. It is fitting that a Republican is bringing it to a close. Although typically thought of as the party most aggressively promoting intervention and free trade, the GOP has long housed some of the nation's most vocal opponents of internationalism – a group now ascendant with the election of Donald Trump.

For much of the 1940s and 1950s, a strong anti-internationalist element was prominent in the GOP, led by Senator Robert Taft. Taft was an American-century sceptic. He believed that if the US got too involved in world events, it would begin to sacrifice its democratic traditions. But as the Cold War heated up, conservative Republicans, the most ardent Taftites, flipped. They became committed "cold warriors", ready to do battle wherever and whenever in order to assert American strength against the Soviets.

No sooner had the Berlin Wall fallen than the anti-internationalists re-emerged. Now called "paleocons", they were led by Pat Buchanan, a former Nixon aide who called for America to return to its roots, to withdraw from its active involvement in the world, to build walls, not bridges. Buchanan did surprisingly well in his run for the GOP nomination in 1992, though he ultimately failed to unseat George H.W. Bush. He was Trump's precursor, a sign that anti-internationalism remained a live cause in the Republican Party.

And so here we stand, a quarter-century after Buchanan's presidential bid, with Trump on his way to the White House.

Overreach in the George W. Bush years are at least partly to blame: the Iraq War and financial collapse were powerful rebuttals to neocon adventurism and global finance.

But those are proximate causes. There is a tectonic shift taking place across the globe. The international institutions and alliances of the Cold War are weakening as the logics and ideals that built them fall out of fashion. Trump campaigned hard against NATO, arguing that the security alliance is too costly and, as currently constituted, no longer in the US' interest.

In recent weeks he has also taken on the United Nations, joined by prominent conservatives and members of his party. After the recent resolution condemning Israel, Washington Post columnist Charles Krauthammer called for the headquarters of the UN to be moved out of the US, half-joking that "Trump ought to find a way to put his name on it and turn it into condos". UN-bashing is nothing new in the GOP, but it would be novel if anti-UN rhetoric were matched with anti-UN politics, particularly withdrawing funds from the organisation.

Add in opposition to the Trans-Pacific Partnership and Trump's support of punishing tariffs, and you have a very different view of America's role in the world. Nor is it just Trump: as his political star has risen, the Republican Party has morphed from the party of free trade to the party of protectionism. Over the course of the past year, opposition to free trade among Republicans swelled from 39 per cent to 61 per cent.

These shifts tell us something about the emerging world order. During the American century, the US and its allies promoted open societies, democracies constrained by civil liberties. American leaders pursued this goal imperfectly but consistently. Even Ronald Reagan's decision to align with right-wing dictatorships in the 1980s was viewed through this lens, drawing from Jeane Kirkpatrick's argument that it was better to side with right-wing dictatorships that might eventually reform into democracies than communist countries that never would.

Trump's anti-internationalism, combined with his preference for authoritarian strongmen, suggests that an open world is no longer the goal, that the future will belong to closed societies where power is the most important metric for partnerships. It is a dramatic change. Fearful of world war, the alliances of the 20th-century were built to defend weak nations from powerful ones. That no longer appears to be a persuasive argument in the 21st-century.

And so we stand on the cusp of a new global order, one whose contours have not yet come into sharp relief, but whose rough edges we can now see. For those who believe in open societies, the portent is grim. The 21st-century may yet be an American century, but if it is, it will not be as the champion of democratic internationalism as Luce had once hoped.

Originally published in The Sydney Morning Herald.