Donald Trump’s renewed hostility toward Canada has revived an old question: how much of the Canada-U.S. relationship rests on friendship, and how much rests on need? The history of energy and environmental diplomacy suggests the answer is mostly the latter.

For decades, Canada and the United States have sustained one of the largest bilateral trading relationships, driven less by affinity than by geography and resources. Shared borders, integrated infrastructure, and abundant energy and water systems made cooperation practical and often unavoidable. The result is a relationship shaped as much by pipelines, rivers, and minerals as by diplomacy or culture.

The two countries have made more than fifty bilateral arrangements, more than any other pair of countries. When it comes to international environmental law, the U.S.-Canada relationship has frequently been a global trendsetter through the creation of accords and settlements such as the Boundary Waters Treaty, the Trail Smelter case, and the Great Lakes Water Quality Agreements. 

Canada has long been the United States’ major foreign energy supplier. After 1945, various types of energy infrastructure (e.g., transmission lines and pipelines) were constructed that bound the two together. And that continues even in the midst of today’s cross border antagonisms: in 2025, more than half of U.S. imports of crude oil, and 99% of natural gas imports, still came from Canada, which remained the largest foreign source of uranium and electricity for the U.S.

The constant contacts, exchanges, and negotiations required to manage day-to-day environmental and energy issues fostered integration and helped anchor the bilateral relationship. Meanwhile, certain resource negotiations, such as the St. Lawrence Seaway, Columbia River Treaty, and acid rain, became punctuated controversies that were the major irritant for a time in government-to-government relations.

Building the Relationship

Natural resources were an important part of the bilateral relationship from the beginning. Most of the early diplomatic relations between the United States and the newly created Dominion of Canada, with Britain the intermediary, revolved around the natural world, particularly fish and water. Environmental diplomacy in the half-century after Canadian Confederation was central to a Canadian-British-American “cleaning of the slate” and creating an amicable continental relationship (as well as better US-British relations). Many of these agreements have proven to be........

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