The U.S. needs a few good allies. Does it still need Canada?

There's a brief, delicious little vignette at the beginning of military historian Tim Cook's latest book that neatly captures the essence of Canada's decades-long national security and defence relationship with the United States.

Speaking in Kingston, Ont. with Prime Minister William Lyon Mackenzie King at his side, President Franklin D. Roosevelt declared that "the people of the United States would not stand idly by if domination of Canadian soil is threatened by any other Empire."

King — who obviously didn't know what the president was going to say ahead of time — was apparently gobsmacked by the assurance, Cook wrote in The Good Allies: How Canada and the United States Fought Together to Defeat Fascism During the Second World War.

Roosevelt's promise, made on Aug. 8, 1938 in the face of rising fascism in Germany, Italy and Japan, has formed the political bedrock of Canada's national security ever since — much to the delight (and chagrin) of Canada's political establishment down the decades.

At the time, King apparently saw the remark for what it was — a historic declaration from a like-minded democracy. He also understood the unspoken aspect.

"It was also a threat of sorts; that the United States would trample Canadian sovereignty if it saw a foreign menace north of the border," Cook wrote.

In 2024, that aspect of Roosevelt's remarks has lost much of its menace. It has been replaced with what former top Canadian national security officials often describe as a deepening sense of exasperation and frustration in Washington with the shiftless attitude in Ottawa that the pledge seems to have created.

Cook documents in his book, often in vivid detail, the genesis of the Canada-U.S. security relationship — lately dominated by American grumbling over Canada's reluctance to hit NATO's military spending benchmark of two per cent of gross domestic product.

His analysis is particularly instructive when you consider the strains on that relationship today, and the persistent sniping of U.S. lawmakers from both sides of the aisle.

As the world once again watches the rise of authoritarian dictatorships, the United States appears to be once again searching for a few good allies. That may be why the exclusion of Canada from the high-tech submarine deal involving Australia, the United States and the United Kingdom still stings so much in Ottawa.

The Second World War was "one of the few times when the United States understood it needed Canada," Cook told CBC News. Canada's geography, mineral wealth and (at the time) untapped industrial potential made it a natural defence partner for the U.S.

Cook suggests that complacency set in on both sides of the border in the decades since, and particularly since the end of the Cold War. Canada's political and institutional establishments have benefited from the American security umbrella, allowing this country to invest generously in social development.

But on the flip side, the United States has had to think about security on its northern border the way it has in the southern region.

"One of the things I have found in reading hundreds of books and documents is that Canada barely registers in any of these discussions in the United States about security issues," Cook said.