The United States and Canada have longstanding plans to invade one another.

Now, whether those plans would actually work is another matter. And it's clear that both nations drew them up mostly as theoretical exercises rather than serious military strategy.

But they exist nonetheless — and have for decades. They're the centerpiece of Kevin Lippert's terrifically fun new book about the history of border tensions between the two nations, War Plan Red, available from Princeton Press. We might think of the US and Canada as having the longest peaceful border in the world, a fact that's been true for decades, but for many, many years, the two countries were constantly either thinking about or actually moving forward with plans to attack.

I spoke with Lippert about the long history behind his book, and we discussed five fascinating facts about the strange story of US-Canadian border squabbles.

This interview has been lightly edited for length and clarity.

1) The US strongly considered annexing Canada after the Civil War

Todd VanDerWerff

So at what point was a US invasion of Canada most likely to succeed?

Kevin Lippert

In the late 19th century, after the Civil War, the US had a large army at its disposal, 500,000 battle-proven men, against a proto–Royal Canadian Mounted Police of about 300 men and 100 livestock. This was amid increasing tensions, particularly between the two great transcontinental railroads, the Canadian Pacific and the Northern Pacific.

Secretary of State [William] Seward had just purchased Alaska and hoped to write out a check for Canada, too. A group of Irish Americans mounted a series of small border raids to try to capture Canada to trade with Britain for Ireland's independence, and early conspiracy theorists suggested that a group of Québecois were involved in Lincoln's assassination.

All this led to a bill introduced in Congress in 1866 to annex Canada. The bill was never voted on, dying a quiet death in committee — plus ça change. Though there were several prior almost-shots-fired skirmishes between the countries, from the Lumberjack War to the Trent Affair, these larger forces of commerce, American Manifest Destiny, and mutual mistrust brought us as close to annexing Canada as we ever were in the second half of the 19th century.

On the other side, in spite of some chest thumping on the part of Canadian nationalists calling themselves "Canada Firsters" — some of whom hoped for a "rattling good war with the United States" to prove their macho credentials — and the massing of troops along the border during the Trent Affair, Canada never mounted a credible threat to annex or invade the United States.

2) The US and the British almost went to war over a pig

Todd VanDerWerff

I was most amazed that one near-miss involved a British military official's pig. Seriously?

Kevin Lippert

Called in one book "the Most Perfect War in History," this is a crazy story of overreaction.

In 1859, Americans and British were both effectively squatting on San Juan Island, off the coast of Washington State, one of many areas with a poorly defined boundary. One day, an American farmer saw a pig rooting around his potato patch, so he naturally shot it dead with his rifle.

"The Pig War was concluded with only one shot fired and one casualty, the hungry British pig"

Quickly, there ensued an argument about liability and compensation, which turned into a military standoff: The British sent five warships and 2,000 men, while the Americans (led by George Pickett — later of the ill-fated Pickett's Charge in the Civil War), rushed in one warship and 500 men, an early version of the Falklands escalation in the 1980s.

With the clear military advantage, British Rear Admiral [Robert L.] Baynes was given the order to engage the Americans, but he refused, saying that "to engage two great nations in a squabble about a pig" was foolish. His calm head presumably averted a rout of the American forces, which likely would have led to a larger conflict. In the end, though, the Pig War was concluded with only one shot fired and one casualty, the hungry British pig.

3) The US thought it was "owed" Canada after the Revolutionary War and took years to get over that idea

Todd VanDerWerff

Why were Americans so sure they could simply waltz into Canada and take it over? There are many times in your book where you talk about an American plan that fell to ruin because of hubris.

Kevin Lippert

This was a combination of several factors. More than one American commander believed he and his troops would be welcomed as liberators by grateful Canadians also hoping to throw off British rule, a mistaken idea on several different occasions (for different reasons).

"The War of 1812 is one sorry Keystone Cops episode after another"

Also, Canada was largely an abjectly poor and agricultural country without a standing army (until 1899), so we thought it would be an easy fight (or march) against a bunch of backwoodsmen (many of whom liked their whiskey). Turns out, we didn't underestimate Canadian (and British) fighting mettle as much as we underestimated our own incompetence. The War of 1812 is one sorry Keystone Cops episode after another.

From almost day one, many Americans believed Canada was somehow "owed" us, that it had slipped between our fingers in the Paris Peace Treaty that ended the Revolutionary War, and that we had only to take what was somehow rightfully ours. It was, as you say, an incredible sense of hubris.

4) Canada wanted to provoke a war the US feared, and the two nations still have (minor) border squabbles from time to time

Todd VanDerWerff

At first glance, the two nations' invasion plans seem very similar. How did they differ?

Kevin Lippert

The main difference was in intention. The Canadians imagined a series of lightning raids followed by a rapid retreat, blowing up roads and bridges behind them — to sting like a bee and run away like a butterfly — in the hope of buying enough time for Britain to sail to its rescue.

The Americans, on the other hand, saw a long war of attrition in which Britain could quickly mass more than 2 million men, noted for their "ability to fight to a finish." Canada's plan looked to provoke the war that American planners feared: a massive buildup of men to our north and ships off our shores.

Todd VanDerWerff

After something like a century of possible military buildup, though, Canada and the US eventually lapsed into peace. How did that happen?

"[War between the US and Canada] would be the political equivalent of setting a fire in your own living room to get rid of the mice"

Kevin Lippert

I think we slipped quietly into peace while nobody was paying attention: Our common interests were too closely aligned — especially after World War II, when we became more or less equal partners in NORAD and sat together worrying about a Soviet nuclear attack.

Also, our economies became so intertwined and our border so porous that the idea of conflict between us became self-defeating. It would be the political equivalent of setting a fire in your own living room to get rid of the mice. It's worth noting, too, that all tensions between us are not gone. There are still several areas of border under dispute, including Machias Seal Island off the coast of Maine and, most touchily, the Northwest Passage.

5) One Canadian thought invading forces would be greeted in the US as, at the least, bartenders

Todd VanDerWerff

What were you most surprised to find in your research for this book?

Kevin Lippert

First, that these plans even existed. From our modern perspective, the very idea seems laughable, but it was all quite serious at the time.

The part I liked the most were the field notes of Lt. James Sutherland "Buster" Brown, author of the Canadian invasion scheme, from his visit to Vermont. [Brown's complete notes are reprinted in Lippert's book.] He found Vermonters affable but fat and lazy, and no impediment to a Canadian invasion.

My favorite line is his quip about Camel's Hump, the mountain in Vermont, to which he said to a local, "You people here are like the camel; you can go seven days without a drink," an allusion to Prohibition: Brown thought invading Canadians might be welcomed as bartenders, if not exactly liberators.

Todd VanDerWerff

So when it all goes down and Canada invades the US, what's your survival strategy?

Kevin Lippert

Shit, where would we go? Canada is most Americans' safety net — if Bush/Obama/Trump/whoever is elected, I'm moving to Canada! — and without it, where to run and hide? France and Italy are already overrun, I think, and not without their own problems. Iceland?

"Wouldn't [Canada invading the US] be like inviting your wealthy, but highly needy and screwed-up uncle to come and live with you in the hope you might someday inherit his money?"

And who would welcome American refugees fleeing a war with its neighbor in this day and age, after we're closing the door on others looking for exactly the same? I joke in the book that a war with Canada would likely be a passive-aggressive economic or cyber one: the shutting down of cellphone networks, internet service, and ATMs. I think most of us, if deprived of wireless access and our ATM machines, would quickly surrender. I suspect I would.

And being part of Canada would have its own benefits: They are a happier and healthier country than ours, with a more functional health care system, a less dysfunctional government, and fewer nut-job politicians. And the world's second-largest supply of oil, and 20 percent of the world's fresh water.

What I don't understand is why Canada would even consider invading the United States: Wouldn't it be like inviting your wealthy, but highly needy and screwed-up uncle to come and live with you in the hope you might someday inherit his money? I suspect a few months in, you'd give [him anything] to have him leave. Maybe the best strategy for assuring our long-term independence from Canada is to shack up with them for a bit. They might even give us the Northwest Passage and Machias Seal Island to go away.

War Plan Red is on sale wherever books are sold.