From the independence of the United States until today, various movements within Canada have campaigned in favour of U.S. annexation of parts or all of Canada. Historical studies have focused on numerous small-scale movements which are helpful in comparisons of Canadian and American politics.
In the early years of the United States, many American political figures were in favour of invading and annexing Canada, and even pre-approved Canada's admission to the U.S. in the Articles of Confederation in 1777. During the American Revolutionary War, the Americans invaded the northeastern and southwestern parts of Canada to achieve this goal, the former which repelled such effort. At the end of the war, the U.S. won its independence and eventually gained territorial control of southwestern Canada, which was later formed into the Northwest Territory. In the War of 1812, the Americans again invaded Canada to avenge the British impressment of American sailors on the high seas and support for Indigenous peoples' resisting American westward expansion, but this was later repulsed, owning much to the reliance on the ill-equipped state militia rather than a standing army.
During and after the American Civil War, several American politicians called for the annexation of Canada because of American anger over Britain's material support for the Confederacy, which one historian asserts lengthened the war by two years, mostly inflicted by British blockade runners delivering arms supplies. Confederate agents operating in Canada received support from a large portion of Canadians throughout the war, allowing the British colony to be used as a base to attack the U.S., such as the St. Albans Raid. In the Alabama Claims in 1872, the U.S. was compensated $15.5 million in war reparations by the British for damages caused only by British-built Confederate commerce raiders, as part of the 1871 Treaty of Washington. Historian Joseph Levitt notes:
Surveys have suggested that a minority of Canadians would potentially support annexation, ranging from as many as 20 percent in a survey by Léger Marketing in 2001 to as few as seven percent in another survey by the same company in 2004.
No elected member of any federal or provincial assembly in Canada, nor any mainstream politician in the United States, openly advocates annexation. Two minor provincial political parties in Canada promoted the concept in the 1980s, but neither attracted widespread support or attention.
Historical annexationist groups
1837
Historical annexationist movements inside Canada were usually inspired by dissatisfaction with Britain's colonial government of Canada. Groups of Irish immigrants took the route of armed struggle, attempting to annex the peninsula between the Detroit and Niagara Rivers to the U.S. by force in the minor and short-lived Patriot War in 1837–1838.
Although the Rebellions of 1837 were motivated in part by this type of dissatisfaction, Canadian resentment of British rule never reached the degree that led to the American Revolution in 1775. Notably, Canada's population growth in the late 18th and early 19th centuries was spurred largely by United Empire Loyalists, who left the American colonies during the Revolution because of their loyalty to Great Britain. In the period from 1790 to 1837, imperial officials repeatedly denounced American-style republicanism and tried to suppress it. The Rebellions themselves were not fought with the goal of annexation, however, but were launched in pursuit of political independence from Britain and liberal social reforms.
Between 1848 and 1854, a significant and articulate minority of conservatives in Upper Canada advocated constitutional changes modelled on the American federal-state system and the US Constitution. They critiqued Canada's imitation of British parliamentary government as both too democratic and too tyrannical. It destroyed the independence of the appointed governor and Legislative Council and further concentrated power in the Cabinet. This critique led many conservatives to argue that the American model of checks and balances offered Canada a more balanced and conservative form of democracy than did British parliamentary government. These "republican conservatives" debated a series of constitutional changes, including annexation to the United States, an elected governor, an elected Legislative Council, a federal union of British North America, and imperial federation, within this framework. These conservatives had accepted "government by discussion" as the appropriate basis for political order.