How the U.S. planned to annex Canada if victorious in a larger war with Britain after World War I

Published: 12 February 2025

By Kenn Oliver
via the National Post website

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In the years after World War I, the United States made several plans for war with other countries, even allies like Britain. A war against the Brits, they envisioned, would begin by attacking Canada. Photo by Andrew Harrer /Bloomberg

It’s become increasingly evident that U.S. President Donald Trump’s rhetoric about Canada becoming the 51st state isn’t just bluster to achieve a more advantageous trade position.

So far at least, he hasn’t mentioned any use of military force to realize territorial expansion and U.S. national security adviser Mike Waltz said he doesn’t think Trump “has any plans to invade Canada.”

But a plan to so do already exists and has for nearly 100 years.

However, War Plan Red, one of several colour-coded war plans devised by U.S. military strategists after the First World War, didn’t identify Canada as a threat. The Yankees’ crosshairs were aimed at the British Empire and the red was a reference to the coats worn by British soldiers during the American Revolutionary War.

In the plan Canada’s hue is crimson and America’s is blue.“Geographically, while CRIMSON provides the RED Empire as a whole with advantageous bases at such widely separated points as to invite an initial dispersion of BLUE armed forces, CRIMSON itself occupies an extremely weak position with respect to BLUE,” reads the plan, first developed in 1925, updated in 1935 and declassified in 1974.“While its territory is of great extent, all well developed parts thereof lie close to the BLUE border; hence, they are especially vulnerable to attack from BLUE.”
Initially, the strategy wasn’t developed with annexation in mind but with a “the best defence is a good offence” mentality that would result in incursions and short-term occupations until the larger conflict with the British was resolved, one way or another.The 1935 update, however, declared that the U.S. would hold any gained territory in Canada “in perpetuity.”“The policy will be to prepare the provinces and territories of CRIMSON and RED to become states and territories of the BLUE union upon the declaration of peace.”If the U.S. lost, they assumed Canada would ask for “Alaska be awarded to her” in return for all the hassle.

Thankfully, Canada remains a sovereign nation, but if the Americans did decide to go to war against Britain, here’s how they envisioned it playing out.

U.S. secretly hoped Canada would ally with Britain

Even though they’d been allies toward the end of the First World War, the relationship between the U.S. and Britain remained frosty in the intervening years — due in no small part to the latter’s massive war debt to America.

Further compounding matters was the British Royal Navy had become the superpower of the sea while American shipbuilding was “in a very depressed state” and years from being revived.

If a war were to break out, the probable cause was assumed to be related to one or both countries interfering with the other’s principal foreign trade relationships or routes.

The drafting of War Plan Red began in 1925. It was declassified in 1974. Photo by National Archives at College Park

And because of both nations’ “proved tenacity” in the theatre of war, the planners “concluded that such a war will be one of prolonged duration.”Planners also assumed Canada would side with King George V and viewed the nation’s neutrality at the outset of any conflict as “always a matter of doubt.”Although they were aware of Canadians’ differing regional opinions on fealty to their colonial sires, in the event of war, the U.S. felt “local feeling would have little effect and the CRIMSON Provinces would take united action.”But the truth is, the Americans considered it advantageous to its cause if Canada allied with the British as it would allow the U.S. to deploy “superior man-power in overrunning” parts of its northern neighbour and causing “suffering to the population and widespread destruction and devastation of the country as well as almost total suppression of normal trade and industry.”

At the time, the U.S. estimated the Canadian Corps and its burgeoning air force to consist of about 100,000 soldiers, non-permanent members and reservists. By 1935, it was noted to be over 135,000.

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