The Longest Undefended Border in the World. Past Tense.

How America spent two centuries building trust with its neighbors and eighteen months burning it down.

America doesn’t need enemies on its borders. It has spent two centuries ensuring it wouldn’t have them — and that security has been so complete, so durable, that most Americans have forgotten it was ever built at all.

That’s the danger of success. You stop seeing the architecture because it’s been load-bearing so long it feels like gravity.

The relationship with Canada alone required surviving the War of 1812, two competing visions of what North America should look like, the pull of competing empires, and a hundred years of careful, unglamorous diplomatic work that nobody writes songs about. The relationship with Mexico required surviving a land grab that México has never fully forgiven, a revolution that spilled across the border, a century of asymmetric economic integration that benefited one side considerably more than the other, and still produced something functional enough to call a partnership.

Neither of these relationships was inevitable. Both of them were chosen, repeatedly, by successive generations of leaders who understood that the alternative — hostile borders, military buildups, intelligence blackouts, the logistical nightmare of treating your neighbors as adversaries — was a cost no serious power could afford.

Then came the clown car.

Trump has threatened to annex Canada. Not metaphorically — to absorb a G7 nation, a NATO ally, a Five Eyes partner, a country that has sent its sons and daughters to fight alongside Americans in every major conflict since the Second World War, into the United States as its 51st state. He has suggested using “economic force” to make it happen, which is the kind of phrase that sounds almost reasonable until you remember it means coercing a democracy into submission. His son floated military force. The administration has not ruled it out.

Photo by Will Goodman on Unsplash

He renamed the Gulf of Mexico the Gulf of America. A body of water that has carried that name for centuries, that borders three sovereign nations, that appears on every map in every country on earth — renamed by executive order because the man in the Oval Office needed to feel large. Mexico did not consent. The world did not comply. American maps now disagree with every other map on the planet. This is what kindergarten geopolitics looks like when it has nuclear weapons behind it.

He has imposed tariffs on Canada and Mexico — not adversaries, not strategic competitors, allies — under a national security framework so tortured that it required ignoring two centuries of integrated economies, shared defense infrastructure, and the basic reality that the three countries manufacture things together, not merely trade them. The auto industry doesn’t have a border. The energy grid doesn’t have a border. The supply chains that feed American families don’t have a border. The tariffs don’t know that. They don’t care.

Let’s focus on the numbers. Canada has 40 million people. Mexico has 130 million. The United States has 335 million. The two countries on America’s borders represent 170 million human beings — more than half the US population — with their own histories, their own grievances, their own long memories, and their own capacity to make American life considerably more complicated than it currently is. These are not small, weak nations that can be absorbed or bullied without consequence. Canada is the largest trading partner the United States has ever had. Mexico is the second. Together they represent the economic architecture that keeps American grocery stores stocked, American factories running, and American energy flowing.

And consider what those numbers mean domestically. There are 11 million Mexican-born people living inside the United States right now. Another 38 million Americans claim Mexican ancestry — roughly 12% of the entire country. There are 820,000 Canadian-born Americans. These are not abstractions. These are people with families on both sides of the borders Trump is threatening to militarize, annex, or rename. These are voters, workers, soldiers, taxpayers. When you threaten to invade Mexico, you are threatening the country of origin of one in eight Americans. When you treat Canada as a subordinate state to be absorbed, you are insulting the birthplace of nearly a million of your own citizens.

The internal political consequences of actually moving on either border don’t require much imagination. They require only arithmetic.

And the arithmetic gets worse when you factor in what happens inside American borders the moment the first boot hits Mexican or Canadian soil. Insurgency researchers estimate that active participation of 2-5% of an affected population is sufficient to make any occupation ungovernable. The American Revolution ran on 40% support. The Iraqi insurgency that bled the US military for a decade drew from a minority of a minority. You don’t need a majority. You need enough.

Two percent of the 38 million Americans of Mexican ancestry is 760,000 people. Five percent is 1.9 million. That is a domestic insurgency larger than the entire active US military, operating inside American cities, with intimate knowledge of infrastructure, supply chains, communication networks, and geography — before a single Mexican national crosses the border in response. And that’s before you account for the neutrals who simply stop cooperating. The DEA loses its informant networks. Border Patrol loses its community relationships. Federal agencies lose their translators, their cultural liaisons, their institutional knowledge. The machinery of governance across the entire American Southwest seizes.

This is not speculation. This is what happens when you make enemies of people who live inside your own borders. The British learned it in 1776. The French learned it in Algeria. The Americans learned it in Vietnam, Iraq, and Afghanistan. The lesson has never changed. The administration simply hasn’t read it.

Now add the native-born Americans who have already declared their opposition. Trump’s approval rating has sunk to between 33% and 39% depending on the poll — with disapproval running as high as 62%. The share of Americans who strongly disapprove is at a second-term high of 46.7%. Only 27% of Americans say they support all or most of his policies. Eight million people turned out for No Kings protests across all fifty states on a single day. Less than one in ten Americans supports sending ground troops anywhere.

The math compounds. You have 11 million Mexican-born residents. 38 million Americans of Mexican ancestry. 820,000 Canadian-born Americans. Add the 150-plus million native-born Americans who currently disapprove of this administration — many of them intensely. At 2% active participation, that’s three million people. At 5%, it’s seven and a half million. That’s not an insurgency. That’s a civil war.

History also has something to say about soldiers ordered to fire on people they recognize as their own. It rarely ends the way the generals planned.

The administration is not planning a military campaign against its neighbors. It is planning a military campaign against a continent — including significant portions of its own population. The people who dreamed this up have apparently never studied what happens when an empire turns its weapons on the people it depends on to operate.

And here is the thought that should keep every armchair annexationist awake at night. Canada and Mexico are not Iraq. They are not Afghanistan. They are not small, distant countries with fractured governments and exhausted populations that can be occupied and managed from a forward operating base. They are vast, modern, literate nations with strong institutional identities, deep reserves of national pride, and — in the case of Mexico especially — a living cultural memory of what American military aggression looks like and what it produces.

An invasion of Canada would trigger an insurgency across 3.8 million square miles of terrain that includes some of the most inhospitable geography on the planet. A country of 40 million people who have just watched their sovereignty violated would not submit. They would resist — in cities, in forests, in the Arctic, across a border so long it cannot be defended let alone controlled. The United States spent twenty years failing to pacify Afghanistan, a country of 40 million people with a fraction of Canada’s resources, institutional capacity, and international support. Canada has all of those things and sits on top of the world’s second largest oil reserves.

Mexico is worse. 130 million people. A country that has fought insurgencies, survived revolutions, and maintained national cohesion through a century of American economic dominance and political interference. A country with a military of 300,000 active personnel, a population with deep experience of asymmetric conflict, and a southern border that connects to the entirety of Latin America. An occupation of Mexico would not be a war. It would be a generational hemorrhage that would drain the American military, treasury, and political will simultaneously — while Iran, Russia, China, and every other adversary currently watching American overstretch accelerated their own ambitions.

The empire would not conquer its neighbors. Its neighbors would consume it.

Now consider the broader strategic picture while all of this is happening. The United States is thirty days into a war with Iran, with Brent crude at $112 and the Strait of Hormuz effectively closed. Russia is running its spring offensive in Ukraine and feeding targeting data to Iranian missiles. China is watching the Indo-Pacific deterrence gap widen with every carrier strike group committed to the Persian Gulf. The Houthis have entered the Iran war and are threatening to close the Bab el-Mandeb. North Korea is quiet in the way that precedes being loud. NATO is fracturing under the weight of American contempt. The G7 is producing confrontations rather than consensus.

This is the strategic environment in which the United States has chosen to threaten its northern neighbor with annexation, rename a body of water shared with its southern neighbor, and DNA-swab a 68-year-old Canadian retiree for wanting to attend a protest.

A competent empire manages its periphery so it can project power at its frontier. It keeps its neighbors close, its alliances intact, and its rear secure. What the Trump administration is doing is the opposite — creating friction on every axis simultaneously, burning the relationships that provide strategic depth, and doing so not out of necessity but out of appetite. Out of the need to perform dominance for a domestic audience that has confused aggression with strength.

This is the same man who called American soldiers buried at Belleau Wood “suckers” and “losers” for having died in service. He doesn’t believe in the people he’s proposing to spend. He believes in the theater of military power without any apparent understanding of or respect for what it actually costs.

Trump and the people around him are not serious in the way that matters. They are serious about performance. About dominance signaling. About the short-term leverage that comes from treating every relationship as a transaction and every ally as a mark. What they are not serious about is the question of what comes after. What the intelligence relationship looks like when Canada decides Five Eyes information shared with Washington ends up serving MAGA political objectives. What the border looks like when Mexico stops cooperating on cartel interdiction because the humiliation finally outweighs the benefit. What NORAD looks like when the junior partner in a joint command has decided the senior partner cannot be trusted.

These are not hypotheticals. They are the logical downstream consequences of the current posture, playing out in slow motion while the administration mistakes silence for compliance and compliance for loyalty.

Sixty percent of Canadians now say they can never trust the United States the same way again. That number will not go back down when Trump leaves office. Trust is not a renewable resource. It accumulates over generations and evaporates in moments. The moment a Canadian retiree was DNA-swabbed at the Blue Water Bridge for wanting to attend a protest — and the officer told him to his face it was because of the nature of his planned activity — that was a moment. Multiply it by every tariff, every annexation joke that wasn’t a joke, every Gulf of America decree, every time a Canadian politician had to stand at a podium and explain to their constituents why they were still cooperating with a government that openly discussed absorbing their country.

Empires have always been good at making enemies. The ones that lasted were good at making something harder — neighbors who chose to stay.

We are losing that. Casually. Irreversibly. By people who inherited something they never had to build and have no idea what its impact on human history portends.