From the very beginning of his presidential aspirations, Donald Trump promised to Make America Great Again. But when was America great? Most commentators assume that Trump, like many nostalgic conservatives, means the initial two decades following World War II — a time of low immigration and a massive surge in economic growth, when many middle-class American workers benefited from well-paid manufacturing jobs.

There's obviously some truth to this. But nearly two and a half years into the Trump administration, it's possible to discern another, more distant object of the president's admiration. That is the 19th century — the time before the United Nations, NATO, and the laws, norms, and institutions of the liberal international order, including the shift toward free trade as an economic ideal and international laws that mandate that national borders be opened to migrants and refugees fleeing suffering and oppression.

Trump wants to Make America Great Again — just like it was during the decades following the Civil War.

Now, it's important not to take the word "wants" in an overly literal way. Trump knows almost nothing about history. I doubt very much that he's consciously choosing to move the country (and the world) back to its state roughly a century and a half ago. Yet this is, in effect, exactly what he's doing, perhaps purely on instinct.

Back in the 1870s, 80s, and 90s (and long before that), states were free actors on the world stage. They pursued their interests unconstrained by uniform rules; they joined alliances, conquered territory, built and defended far-flung empires, and waged wars at will; and they imposed tariffs on each other in order to raise revenue, gain economic advantage, and conduct foreign policy.

As this anarchic system continued to evolve into the early 20th century, with different blocs of countries joining competing military alliances, it led the great powers to the Great War that ultimately left the system in tatters. At first, American president Woodrow Wilson attempted to substitute a League of Nations and a system international law for the lawless competition of the 19thcentury. That was scuttled by the rise of the totalitarian empires that were ultimately defeated by the United States and its allies on the battlefield in World War II.

After the war, Wilson got the posthumous last laugh. The United Nations, the International Monetary Fund, the World Bank, the Universal Declaration of Human Rights, the UN convention on refugees, the founding of NATO (to defend the vulnerable liberal democracies of Western Europe against Soviet expansionism) — all of these and many more international laws, institutions, norms, and agreements have little by little bound the nations of the world together in a web of rules designed to impede the free action of states and bend them toward greater openness — free trade, the free movement of peoples — as well as toward greater adherence to rationalized decision-making.

The U.S. invasion of Iraq was the exception that proved the rule — or rather, it was the exception that proved the rule of rules. Before acting to take down the regime of Saddam Hussein, America felt it had to make its case before the world, which it did, proposing itself as a means to the enforcement of imperfectly enforced UN resolutions. Much of the world was unpersuaded by the reasoning and evidence, but the U.S. acted anyway on the grounds that it knew best how to uphold international law, even in defiance of international consensus. The result was widely viewed as an act of lawnessness undertaken in the name of law-abidingness.

The Trump administration has done something similar twice, when, on two occasions, it (lightly) bombed Syria in response to its use of chemical weapons against civilian populations in the country's civil war. Both times the U.S. justified its actions in terms of the need to uphold international laws and norms on the use of such weapons and punish states that transgress them — even though no one empowered the United States to act as such a unilateral judge, jury, and executioner of global justice.

Other than those times, however, Trump's actions around the world have been conducted in a very different mode. Trump despises constraints of any kind. He longs to be a free agent, a mob boss backed up by the most powerful military in the world — acting, threatening, arm-twisting, negotiating, and striking (almost always bilateral) deals with allies and enemies alike, all of whom he views as adversaries and rivals to his own and America's power. (In Trump's mind, the two are identical.)

Regardless of the concessions Trump did or did not extract from Mexican president Obrador in their recent standoff over Central American migration and refugees, that conflict was important because it displayed something we haven't seen in quite some time — the imposition of tariffs, not primarily as a means of negotiating concessions on trade, but as a tool for conducting foreign policy. Whereas the U.S. has spent decades attempting to uphold the liberal international order by imposing economic sanctions on recalcitrant nations and by dangling the promise of "most favored nation" trading status before countries on the periphery of the liberal-democratic world, Trump appears willing and eager to use the threat of tariffs to coerce other countries into bending to our will and serving our national interests, narrowly construed.

That needs to be seen for what it is — a reversion to an older (some will say archaic) style of statecraft, one that takes its cues not from universal-humanitarian moral principles, international law, or the expectations of the liberal institutions the United States created in the aftermath of the Second World War. It takes its cues, instead, from whatever benefits the United States, full stop.

None of this necessarily implies that the way Donald Trump defines our national interests makes sense. He could have been (and I think he was) foolish to tear up the Trans-Pacific Partnership and to withdraw from the Paris Climate Accord and the Iran Nuclear Deal.

But (assuming he avoids a major war) the way Trump conducts himself on the world stage could well prove to be even more momentous for the future of the planet than the substance of his specific policy commitments. Trump is acting like a 19th-century bull in a china shop overseen by 21st-century technocrats in Brussels and Turtle Bay. With him setting the country's tone, the U.S. is acting less like a benign hegemon out to enforce the rules and more like the greatest of the world's great powers — one that's eager to compete for comparative advantage against all the others.

When The Trump Show is over, will American voters want to go back to the future that followed the ruthless rivalries and vicious wars of the 19thand early 20thcenturies? Or will they be more interested in refining Trump's outlook on the world — treating the liberal internationalism of the postwar decades as an anomaly and looking back, instead, to earlier times for a model of how powerful states should comport themselves, seek advantage, and achieve "greatness" in the world?

Few questions raised by the Trump presidency are more portentous than these.