Donald Trump’s Arctic strategy has been 500 years in the making.

When Christopher Columbus set sail across the Atlantic in 1492, he intended to find a direct path from Europe to Asia. He didn’t, of course — but the first transatlantic explorer to sail under an English flag, John Cabot, tried again a few years later and became the first modern explorer to reach what is now Canada.

The commercial potential of the Northwest Passage was obvious from the start, but even once explorers at last figured out how to thread their way through the Arctic’s ice and islands, there was no possibility of developing the route: The sea ice was just too dense.

Until now, that is: Warmer temperatures and 21st-century technology put a trade route the world has sought for centuries within reach — but whose? Canada claims the passage as its own territorial waters.

America, like most of the world, has never accepted that assertion. The future of what one day may be the planet’s most important shipping lane is being decided today.

China is literally testing the waters. In 2017, the Chinese used a research vessel to confirm that cargo ships can now make it through the passage.

Since then, Beijing has focused most of its Arctic attention on its relationship with Russia, whose northeastern sea routes are already well developed. Yet there’s no doubt about China’s long-range intentions.

One former Canadian security official, professor Stephanie Carvin, told the CBC in September that China “has an ambitious plan to basically control a lot of the rare-earth elements and mining.”

President Trump recognizes the dangers here. Canada is heavily reliant on America’s intelligence capabilities and military strength, but Canadian security depends on Canadian politics, and that’s the weak link. Governments in Ottawa have failed to meet Canada’s NATO commitments to spend at least 2% of GDP on defense.

Prime Minister Mark Carney’s courtship of Chinese trade in recent weeks highlights how economically vulnerable America’s northern neighbor is.

The Northwest Passage and the Arctic’s mineral resources are vital to the economic security and military defense of America, Europe and Canada alike.

Trump’s hardball diplomacy with Ottawa puts a strain on America-Canada relations, but they also force Canadian leaders to think about the country’s ultimate choices. If Trump seems like a bully, what can Ottawa expect from China and Russia as the Northwest Passage’s potential is realized?

Americans, too, have to face reality: We can’t afford to be complacent about how this neighbor and ally governs the waters it claims but can’t secure.

Canada should take a lesson from Greenland’s experience: Trump seemed to demand nothing less than Denmark’s surrender of the territory to America, but once he’d succeeded in shocking everyone into thinking about the most basic questions of sovereignty and security, he used the opportunity to strengthen America’s commitments to Greenland’s defense.

His approach to Canada is similar — Trump is not trying to repeat James Madison’s folly in the War of 1812, when America actually tried to annex Canada. Instead, he’s asking Canada’s leaders to acknowledge they can’t take our trade and defense for granted.

Today the Arctic is the free world’s frontier, and Canada can keep it safe only by treating America as a partner, not a piggy bank.