Lawrence Herman is a former Canadian diplomat who practices international trade law at Herman & Associates. He is also a Senior Fellow of the C.D. Howe Institute in Toronto.

In the years since the Second World War, Canadian foreign policy was built on three fundamental pillars: First, the maintenance of strong relations with the United States; second, faith in the United Nations-Bretton Woods system, the multilateral institutions that were built after the war; and third, agreements and alliances with other Western liberal democracies, including our NATO partners.

That structure has been severely shaken – not only by the America First policies of U.S. President Donald Trump’s administration, but also by the shifting dynamics of relationships with China, Europe and the Middle East.

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Canada’s crucial relationship with the United States has been more and more strained as the year progressed, notwithstanding the three-way agreement in principle with the United States and Mexico to replace NAFTA. And the year ended with a major altercation with China after the United States requested that the Canadian government arrest Huawei executive Meng Wanzhou, who is now facing extradition. And while those are the two most difficult foreign policy challenges Canada faces after a dreadful 2018 in terms of foreign affairs and trade, they’re hardly the only ones.

Russia’s annexation of Crimea and the Canadian response has resulted in the frostiest relationship between the two countries since the demise of the Soviet Union. Chrystia Freeland, Canada’s foreign minister, is denied entry to that country, a situation without precedent.

Then there are the difficulties with Saudi Arabia, precipitated by a tweet from Ms. Freeland demanding the Saudis immediately release two jailed dissidents. While Canada has good reason to condemn Saudi Arabia’s human rights abuses, the Saudis responded by ordering the expulsion of Canada’s ambassador and declaring him a persona non grata – the most extreme action in international diplomacy short of a complete rupture. And since Canada has no political relationship with Iran – Stephen Harper’s government broke off diplomatic ties with the renegade country in 2012 – Canada has been frozen out of the two most influential nations in the Middle East, seriously weakening its entire regional policy.

Meanwhile, its political gulf with eastern European countries only continues to grow. In countries such as Hungary and Poland, the resurgence of right-wing populist governments has created differences that are inevitably reflected in tenser political relationships. And the lack of respect for democratic values in Turkey, given the increasingly autocratic nature of the Erdogan government, has also weakened Canada’s influence with the important regional player and NATO ally.

Meanwhile, the political turmoil inside three of Canada’s important liberal democratic allies – the United Kingdom, France and Germany – has led to foreign-policy complications of a different sort as these countries turn inward to deal with their own domestic problems, weakening the informal alliance that was so solid and promising when Premier Justin Trudeau took office in 2015.

These shifts in the international situation have left Canada struggling to find its way forward in a fractured world where old relationships, assumptions and precepts are weakened or no longer hold. And that’s all compounded by major changes on the multilateral front, including the United States' withdrawal from global leadership within the United Nations and from its Paris climate accord, as well as the Trump White House’s attacks on the World Trade Organization.

The result: Canada finds itself bereft of long-standing alliances and in many ways alone.

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Looking ahead into 2019, things seem uncertain at best, and could even deteriorate further. As long as Mr. Trump is in office, the United States will continue to be an uncertain ally, especially on the trade front. Efforts to end the United States’ national-security surcharges on Canadian steel and aluminum remain stalled. U.S. trade actions against Canadian softwood lumber and steel products continue, too.

With protectionism reigning in the White House, Mr. Trump has started to look for external scapegoats to shore up his political base ahead of the 2020 presidential election. Canada’s imbroglio with China won’t easily or quickly be resolved, as the long and complex extradition proceedings for Ms. Meng continue.

All these shifting dynamics mean that the premises that underlie Canada’s longstanding foreign and trade policy are no longer valid. And building a new strategic framework in a vastly altered and hostile world will be a major challenge for Canada as the storm clouds continue to gather in 2019.