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US–Canada Relations

One shared air-defense command, a demilitarized border since 1817, the largest foreign source of US crude oil by a wide margin — and a trade relationship renegotiated under tariff threat often enough that the disputes have numbered rounds.

8 documented events, earliest first. Every card carries its evidence tier and its own sources.

April 28–29, 1817

The Rush–Bagot Agreement

EMPIRICAL

An exchange of notes between the acting US secretary of state and the British minister, after the War of 1812, limiting each side to a handful of small armed vessels on the Great Lakes and Lake Champlain. Ratified by the Senate in 1818. Adjusted by exchanges of notes in the twentieth century; never revoked.

One vessel of no more than 100 tons and one 18-pound gun on Lake Champlain and on Lake Ontario; two on the upper lakes.

What it changed

Demilitarized the longest border on earth before either side had the means to fortify it. The oldest arms-limitation arrangement the United States observes, and the precondition for every later integration: a defense partnership can only be built across a border nobody is defending.

Sources

US Department of State, Office of the Historian, "Rush-Bagot Pact, 1817 and Convention of 1818" · government
Britannica, "Rush–Bagot Agreement" · academic

January 11, 1909

The Boundary Waters Treaty

EMPIRICAL

Signed between the United States and Great Britain on Canada's behalf, the treaty set rules for the use and apportionment of waters along the border and created the International Joint Commission — three commissioners from each country — to apply them. Diversions require the Commission's approval.

What it changed

The first permanent joint institution the two countries built, forty years before NORAD. It made shared water a matter of standing procedure rather than diplomacy, and it is the model the Columbia River Treaty and the Great Lakes agreements followed.

Sources

International Joint Commission, "Boundary Waters Treaty" · government
The Canadian Encyclopedia, "Boundary Waters Treaty" · academic

August 18, 1940 and April 20, 1941

Ogdensburg and Hyde Park

EMPIRICAL

At Ogdensburg, Roosevelt and King created the Permanent Joint Board on Defence to study the sea, land and air defense of the northern half of the hemisphere. At Hyde Park eight months later they agreed that each country would buy the defense goods the other was best placed to make, and that American components in Canadian-built equipment for Britain would count under Lend-Lease.

What it changed

Integrated defense planning and defense production before the United States was at war. The Board still meets; the Hyde Park principle — one continental defense-industrial base — is what the later Defence Production Sharing arrangements formalized.

Franklin D. RooseveltWilliam Lyon Mackenzie King

Sources

June 29, 1949

The CANUSA agreement

EMPIRICAL

A bilateral signals-intelligence sharing agreement between Canada and the United States, accepted by the chairman of the US Communications Intelligence Board in a letter of June 29, 1949. It sits beside the 1946 UK–US agreement and is the instrument that made Canada a full partner in what became the Five Eyes.

What it changed

Intelligence integration at the level of raw signals, in peacetime, with a partner whose geography covered the Arctic approaches. The Canadian signals agency exists in its postwar form because this agreement gave it a reason to.

Sources

Operational September 1957; agreement signed May 12, 1958

NORAD

EMPIRICAL

The North American Air Defense Command placed the continental air defenses of both countries under one binational commander at Colorado Springs, with a deputy from the other country. Renamed Aerospace in 1981; renewed in perpetuity in May 2006 with a maritime-warning mission added and a review at least every four years.

Renewed March 1968, 1973, 1975, 1980, 1981, 1986, 1991, 1996, 2000; in perpetuity from May 2006.

What it changed

The only standing arrangement in this section in which two sovereign militaries share a single operational command. Canadian officers have ordered US aircraft; the reverse is routine. It is also why a Canadian decision on weapons became an American concern in 1963.

Sources

North American Aerospace Defense Command, "NORAD Agreement" · government
The Canadian Encyclopedia, "NORAD" · academic

January 16, 1965

The Auto Pact

EMPIRICAL

Signed at the LBJ Ranch by Johnson and Pearson, the Canada–United States Automotive Products Agreement removed tariffs on vehicles and parts between the two countries for the manufacturers, in exchange for Canadian production guarantees. Automotive trade went from $730 million in 1961 to over $3.3 billion in 1967. Found contrary to WTO rules and ended in 2001.

What it changed

The first sectoral integration of the two economies, and the template: a single continental production line, managed by agreement. The automotive rules of origin fought over in the USMCA are the descendants of this document.

Lyndon B. JohnsonLester B. Pearson

Sources

Government of Canada, treaty text, "Agreement concerning Automotive Products" · primary
The Canadian Encyclopedia, "Canada-US Auto Pact" · academic

January 1, 1989; January 1, 1994; July 1, 2020

Free trade in three instruments

EMPIRICAL

The Canada–US Free Trade Agreement took effect in 1989 after a Canadian election fought on it; NAFTA added Mexico in 1994; the USMCA (CUSMA in Canada) replaced NAFTA in 2020 after renegotiation under threat of US withdrawal, with a joint review every six years.

What it changed

Made the two economies one market in most goods, which is what gives a tariff threat its force: the party with the smaller economy and the larger export share has more to lose from the same measure.

Sources

Congressional Research Service, "The United States-Mexico-Canada Agreement (USMCA)" (R44981) · government
USTR, United States-Mexico-Canada Agreement · government

2024

Crude oil: 62 percent of US imports

EMPIRICAL

US crude oil imports from Canada averaged 4.1 million barrels a day in 2024, a record and 62 percent of all US crude imports; Mexico, Saudi Arabia and Venezuela together supplied 14 percent. In 2005 Canada's share was 16 percent. Much of the flow is heavy crude that Midwest and Gulf Coast refineries were configured to run.

4.1 million b/d, 62% of US crude imports, 2024 (EIA data via the Canada Energy Regulator).

What it changed

The energy relationship has no treaty under it; it is pipelines and refinery configuration. That is why a 10 percent tariff on Canadian energy in 2025 was set lower than the 25 percent on everything else — the dependency runs toward the United States in this one channel.

Sources

Standing arrangements rather than events — what the relationship is, as opposed to what happened to it. Where an arrangement runs in one direction, the card says so.

Defense·May 12, 1958; in perpetuity from May 2006

NORAD

IN FORCE

A single binational command for aerospace warning, aerospace control and maritime warning over the continent, with a US commander and a Canadian deputy commander.

Who depends on whom

Both directions, and unequal in kind: the United States supplies most of the sensors and interceptors; Canada supplies the territory the warning depends on. Neither can run continental air defense without the other's airspace.

Sources

NORAD, "NORAD Agreement" · government

Intelligence·June 29, 1949

CANUSA and the Five Eyes

IN FORCE

Exchange of signals intelligence at the level of raw collection, and the division of the world into collection responsibilities among the five partners.

Who depends on whom

Runs toward Canada in volume — the US agencies collect far more — and toward the United States in geography: the Arctic and the northern approaches are Canadian coverage.

Sources

Communications Security Establishment Canada, "CANUSA" · government

Trade·July 1, 2020; joint review every six years

USMCA / CUSMA

IN FORCE

Tariff-free trade in most goods among the three countries, with automotive rules of origin, dairy access provisions and dispute panels.

Who depends on whom

Asymmetric: about three-quarters of Canada's exports go to the United States; a far smaller share of US exports go to Canada. The 2025 tariffs were imposed on a partner inside this agreement, under a different statute, which is the point the Canadian government made.

Sources

Legal·January 11, 1909

The Boundary Waters Treaty and the International Joint Commission

IN FORCE

Joint approval of diversions and uses of boundary waters; investigation and recommendation on any question either government refers; the Great Lakes water-quality agreements sit under it.

Who depends on whom

Both directions and equal by design — three commissioners each, decisions by majority, no veto. The one instrument in the section built to be symmetrical.

Sources

International Joint Commission, "Boundary Waters Treaty" · government

Legal·Ratified 1961; implemented 1964; agreement in principle on modernization July 11, 2024

The Columbia River Treaty

CONTESTED

Canadian storage dams regulate the Columbia for US flood control and hydropower; the United States returns a share of the downstream power benefit to Canada. Eighteen rounds of negotiation between 2018 and 2023 produced an agreement in principle to reduce the power returned, pay for flood control, and add ecosystem flows.

Who depends on whom

Runs toward the United States in water and toward Canada in payment. "Contested" because the modernized terms were agreed in principle, not ratified, and the 2025 tariff dispute arrived before they were.

Sources

Congressional Research Service, "Columbia River Treaty" (R43287) · government
White House, statement on the agreement in principle, July 11, 2024 (DCPD-202400597) · government

Legal·December 2004; extended to the whole border March 2023

The Safe Third Country Agreement

IN FORCE

Each country treats the other as safe for refugee claimants: a person who arrives in one may not claim asylum in the other at a land border. The Supreme Court of Canada held unanimously in June 2023 that the arrangement does not breach the Charter's section 7, and left the section 15 equality question open.

Who depends on whom

Runs toward Canada in practice: the northbound flow of claimants is the one the agreement was written to manage.

Sources

Defense·1817

Rush–Bagot

IN FORCE

Almost nothing — which is the point. Naval armament on the Great Lakes is limited to a few small vessels. Both governments have agreed since the 1940s that it does not cover coast guard and customs vessels.

Who depends on whom

Mutual and symmetrical. The demilitarized border is the thing everything else on this page assumes.

Sources

US Department of State, Office of the Historian · government

Trade·No treaty

Energy — no instrument, a flow

IN FORCE

Nothing is permitted; it happens. Four million barrels a day of crude, plus natural gas, electricity and uranium, moving on pipelines and transmission lines built for it. Keystone XL, the one addition that needed a presidential permit, had it granted in 2017, revoked in 2021, and the project was abandoned.

Who depends on whom

Runs toward the United States: Canadian heavy crude has few other buyers, and US refineries in the Midwest have few other suppliers of that grade. Both are locked in by hardware.

Sources

Canada Energy Regulator, 2024 Canada-U.S. energy trade · government

The moments the relationship failed. These are on the page deliberately: a relations page that lists only cooperation is advocacy. A rupture is where the real terms become visible.

January 30 – February 6, 1963

The State Department undercuts a Canadian government

EMPIRICAL

Canada had accepted Bomarc missiles under NORAD but Prime Minister Diefenbaker would not decide whether to accept the nuclear warheads they were built for. After an equivocal speech in the Commons, the State Department issued a press release on January 30, 1963, stating that Canada had "not yet proposed any arrangement sufficiently practical to contribute effectively to North American defence." Cabinet ministers resigned; the government fell on a confidence vote on February 5; Diefenbaker lost the April election.

What it revealed

That a shared command carries a shared veto: once Canadian air defense was integrated under NORAD, a Canadian weapons decision was treated in Washington as an American one, and Washington was willing to say so publicly. The opposition leader reversed his own position on the warheads within days and accepted them after winning.

Aftermath

Pearson's government took the warheads in 1963. Canada later gave them up — the last were withdrawn in 1984. The episode is the standard reference for the cost of integration on the smaller side.

John DiefenbakerJohn F. KennedyLester B. Pearson

Sources

April 2–3, 1965

Pearson at Temple University

EMPIRICAL

Accepting a peace award in Philadelphia, Pearson proposed "a measured and announced pause" in the bombing of North Vietnam. Johnson summoned him to Camp David the next day and, by the accounts of those present, berated him for an hour and took him by the lapels.

What it revealed

The limit of permitted dissent: a Canadian prime minister could decline to send troops, but could not say in the United States what the United States should do. The speech was mild; the reaction defined the boundary.

Aftermath

No instrument changed. Canada stayed out of the war and sold it materiel under the Defence Production Sharing arrangements throughout.

Lester B. PearsonLyndon B. Johnson

Sources

August 15, 1971 – 1972

The Nixon surcharge and the Third Option

EMPIRICAL

Nixon closed the gold window and imposed a 10 percent surcharge on dutiable imports. Canada, which had been exempted from earlier US measures in 1963 and 1965, asked for an exemption and was refused. In 1972 the external affairs minister, Mitchell Sharp, published three options for Canadian policy; the third, reducing vulnerability by diversifying away from the United States, became government policy.

What it revealed

That the special treatment Canada had come to expect was a courtesy, not a term, and could be withdrawn without notice. The Third Option was the first formal Canadian attempt to reduce the dependency; it is generally judged to have failed, which is itself evidence of how deep the integration already was.

Aftermath

The surcharge was lifted in December 1971. Fifteen years later Canada chose the opposite of the Third Option and negotiated free trade.

Richard NixonMitchell Sharp

Sources

1982 – present

Softwood lumber, rounds I through V

EMPIRICAL

US producers petitioned for countervailing duties on Canadian lumber in 1982, alleging that provincial stumpage fees were a subsidy. The dispute has since run in five numbered rounds: a 1986 memorandum with a 15 percent export tax, a 1996 quota agreement, duties from 2001 until the 2006 Softwood Lumber Agreement, and a fifth round since that agreement expired on October 12, 2015. Duties have been imposed, litigated under NAFTA and WTO panels, and partially refunded, repeatedly.

What it revealed

That free trade had an exception written into its practice from the start, and that the exception is driven by a domestic industry rather than by the state of the relationship. The dispute has outlasted eight presidents and the agreements meant to end it.

Aftermath

No settlement. Combined duties on Canadian softwood were raised again in 2025. The dispute recurs on the cycle of US housing demand and Commerce Department reviews.

Sources

Congressional Research Service, "Softwood Lumber Imports from Canada: Current Issues" (R42789) · government
The Canadian Encyclopedia, "Softwood Lumber Dispute" · academic

March 17, 2003

Canada declines Iraq

EMPIRICAL

Two days before the invasion, Prime Minister Chrétien told the House of Commons: "If military action proceeds without a new resolution of the Security Council, Canada will not participate." He had not told Washington first. Records released later show Canada had been prepared to send ships had the Security Council authorized action.

What it revealed

The relationship could absorb a public refusal on a war, where it could not absorb a public suggestion in 1965 — because by 2003 the refusal was conditioned on the UN, a position Canada had held since Korea, and because Canada was already in Afghanistan. The cost was personal, to the two leaders, rather than structural.

Aftermath

Canadian forces stayed in Afghanistan until 2014. No instrument changed. The Bush–Chrétien relationship did not recover.

Jean ChrétienGeorge W. Bush

Sources

June 1, 2018; February 1, 2025 – February 20, 2026

Tariffs on the defense partner: 2018 and 2025

EMPIRICAL

In 2018 the United States ended Canada's exemption from Section 232 steel and aluminum tariffs, imposed on a national-security rationale; Canada retaliated on $16.6 billion of US goods, and the duties were lifted in May 2019. On February 1, 2025, Executive Order 14193 invoked the International Emergency Economic Powers Act to impose a 25 percent tariff on Canadian goods and 10 percent on Canadian energy, citing fentanyl trafficking as an "unusual and extraordinary threat"; the rate on non-USMCA goods was later raised to 35 percent. The same period saw repeated statements by the president that Canada should become a US state. On February 20, 2026, the Supreme Court held 6–3 in Learning Resources v. Trump that IEEPA does not authorize tariffs at all.

What it revealed

That the trade instrument could be used against the NORAD partner on a security rationale the partner called false, and that the agreement the two had signed in 2020 did not prevent it — a different statute did. The restraint in the relationship turned out to be in US domestic law, not in the bilateral instruments.

Aftermath

The Court decided only the statutory question and left refunds and remedies to the Court of International Trade; Section 232 duties, which rest on a different statute, were untouched. The 2026 USMCA joint review is the next scheduled test.

Donald TrumpJustin TrudeauMark Carney

Sources

January 20, 2021

Keystone XL revoked

EMPIRICAL

On his first day in office, President Biden signed Executive Order 13990, revoking the presidential permit for the Keystone XL pipeline that had been granted in 2019. TC Energy, after consulting the government of Alberta, terminated the project on June 9, 2021.

What it revealed

That the energy relationship, the one with no treaty under it, is governed on the US side by a single permit the president can withdraw — and that a Canadian province's investment in the line had no standing against that.

Aftermath

Existing pipelines carried record volumes anyway; the 2024 import figure is the aftermath. Alberta's claim for its investment was dropped with the litigation.

Joe Biden

Sources

Continuous relationship since 1940 — The Ogdensburg Agreement

On August 18, 1940, with France fallen and Britain under air attack, Roosevelt and Mackenzie King met at Ogdensburg, New York, and created the Permanent Joint Board on Defence — permanent by name, and still sitting. It is the point at which the defense of the continent became a joint undertaking rather than two national ones, and every later instrument (Hyde Park, NORAD, the intelligence agreements) descends from it. The border had been settled a century earlier; what began in 1940 was integration.

What is documented: the Rush–Bagot agreement of 1817 that limited naval forces on the Great Lakes and has never been revoked; the 1909 Boundary Waters Treaty and the International Joint Commission it created; Ogdensburg in 1940 and the Hyde Park Declaration of 1941 that integrated defense production; the CANUSA signals-intelligence agreement of 1949; NORAD, formalized in 1958 and renewed in perpetuity in 2006; the Auto Pact of 1965, the Free Trade Agreement of 1989, NAFTA in 1994 and the USMCA in 2020; crude oil imports from Canada of 4.1 million barrels a day in 2024, 62 percent of all US crude imports; and a softwood lumber dispute that has run in five numbered rounds since 1982. The ruptures run both ways — Washington publicly undercut a Canadian government in 1963 and it fell; Ottawa declined Vietnam escalation in 1965 and Iraq in 2003 — and the one that is still open is the 2025 use of emergency tariff powers against the defense partner, powers the Supreme Court held in February 2026 the statute never granted.

This page covers structure, not sentiment. The relationship is usually described as the closest the United States has; the page tests that against the instruments, and finds it true in defense and intelligence, true in energy, and repeatedly suspended in trade. Where the two readings conflict, the cards say so rather than the summary.

US–Canada Relations — UET Library

US–Canada Relations

The Rush–Bagot Agreement

The Boundary Waters Treaty

Ogdensburg and Hyde Park

The CANUSA agreement

NORAD

The Auto Pact

Free trade in three instruments

Crude oil: 62 percent of US imports

NORAD

CANUSA and the Five Eyes

USMCA / CUSMA

The Boundary Waters Treaty and the International Joint Commission

The Columbia River Treaty

The Safe Third Country Agreement

Rush–Bagot

Energy — no instrument, a flow

The State Department undercuts a Canadian government

Pearson at Temple University

The Nixon surcharge and the Third Option

Softwood lumber, rounds I through V

Canada declines Iraq

Tariffs on the defense partner: 2018 and 2025

Keystone XL revoked

Does the defense integration survive the trade relationship being used against it?

What replaces the IEEPA tariffs, and does the replacement reach Canada?

Is the energy dependency leverage for Canada, or a lock for both?

Was the Third Option wrong, or early?

US–Canada Relations

The Rush–Bagot Agreement

The Boundary Waters Treaty

Ogdensburg and Hyde Park

The CANUSA agreement

NORAD

The Auto Pact

Free trade in three instruments

Crude oil: 62 percent of US imports

NORAD

CANUSA and the Five Eyes

USMCA / CUSMA

The Boundary Waters Treaty and the International Joint Commission

The Columbia River Treaty

The Safe Third Country Agreement

Rush–Bagot

Energy — no instrument, a flow

The State Department undercuts a Canadian government

Pearson at Temple University

The Nixon surcharge and the Third Option

Softwood lumber, rounds I through V

Canada declines Iraq

Tariffs on the defense partner: 2018 and 2025

Keystone XL revoked

Does the defense integration survive the trade relationship being used against it?

What replaces the IEEPA tariffs, and does the replacement reach Canada?

Is the energy dependency leverage for Canada, or a lock for both?

Was the Third Option wrong, or early?