If America's allies needed one more reminder of the threat Washington's new boss poses to the international order that previous American leaders built, President Donald Trump just gave it to them. Nearly every word of his inaugural address aggressively underlined his campaign's central message: Screw you, world. America First.

In Mr. Trump's telling, the United States is not the leader of the postwar international order. Instead, it is its chief victim. The idea resonated powerfully with a large number of American voters. That's why his first act as President was to restate it. That's why he is going to pursue America First over the next four years. Mr. Trump has understood something profound about his supporters and their fears, and his promise to benefit America by sticking it to everyone else is not just a rhetorical device.

"We assembled here today are issuing a new decree to be heard in every city, in every foreign capital, and in every hall of power. From this day forward, a new vision will govern our land. From this day forward, it's going to be only America first, America first.

Story continues below advertisement

Barrie McKenna: Trump's pledge to put America first leaves Canada behind on jobs and trade (subscribers)

Opinion: Canada must remain firm in the face of 'America First'

Read more: What does the Trump era mean for Canada? A guide to what's coming

"Every decision on trade, on taxes, on immigration, on foreign affairs will be made to benefit American workers and American families. We must protect our borders from the ravages of other countries making our products, stealing our companies and destroying our jobs. Protection [he almost certainly meant to say "protectionism"] will lead to great prosperity and strength."

So that's the agenda facing NATO, the European Union, Japan, the rest of the democratic world – and Canada. The United States has provided global leadership for 75 years. It has always looked out for its interests, and then some. But its leaders generally understood that international affairs, including trade, did not have to be a zero-sum game. For America to win, it did not mean that others had to lose. In economic theory, trade is capable of being a win-win arrangement. In Trumpian theory, apparently not.

The Free Trade Agreement between Canada and the U.S. was not an American plan to strip Canada's economy. NAFTA was not a plot to crush America's neighbours. The World Trade Organization was not a scheme to benefit American exporters at the rest of the world's expense. And that's Mr. Trump's chief complaint about America's trade agreements: They failed to put America First.

After the Second World War, the United States briefly considered keeping the peace by turning Germany and Japan into enfeebled, agricultural societies. Instead, it rebuilt Western Europe with the generosity of the Marshall Plan, and transformed Japan into a model democracy. It saw the prosperity and success of its former enemies as the best guarantor of America's own peace, prosperity and leadership.

Story continues below advertisement

It was one of history's greatest acts of enlightened self-interest. Europe and Japan boomed. So did trade. So did the United States. America was the free world's leader because it did more than just put America First.

Mr. Trump, like the men who created the American-led, postwar global order, has trade at the centre of his world view. But it's not free trade. In his telling, deals have one winner and one loser. Somebody is getting taken to the cleaners, and somebody else is making out like a bandit. The idea that trade is like a poker game, where one player wins the pot and everyone else goes home with an empty wallet, appears to constitute almost the entirety of his view of international relations.

And though he never mentions Canada, this country runs the risk of becoming one of the chief pawns in Mr. Trump's political theatrics.

Canada's economy is highly trade-dependent, much more so than the U.S. And we trade far more with America than with any other country. Our industries, from oil to auto manufacturing, are highly interconnected. That, after all, was precisely what the FTA and NAFTA were designed to achieve. Even if we are not the main target of Mr. Trump's administration, we are in danger of being side-swiped as the American ship of state makes a sharp turn.

"America will start winning again," said Mr. Trump in his inaugural. "Winning like never before. We will bring back our jobs. We will bring back our borders. We will bring back our wealth."

In President Trump's telling, that means taking jobs and wealth "back" from America's trading partners. China and Mexico are the countries he names most often. But when Mr. Trump proclaimed his "new decree," promising to be heard "in every foreign capital," he was bellowing most loudly at America's leading allies and trading partners: Europe, Japan, Canada.

Story continues below advertisement

The man who can't say an unkind word about Vladimir Putin, an actual antagonist to America's interests, is happily threatening trade war with America's actual friends. If President Trump's government vigorously pursues America First, it spells the end of the American Century, and the dawn of something darker.