Since the conclusion of the War of 1812, historians have long debated the relative weight of the multiple reasons underlying its origins.

During the nineteenth century, historians generally concluded that war was declared largely over national honour, neutral maritime rights and the British seizure of neutral ships and their cargoes on the high seas. This theme was the basis of President James Madison's war message to Congress on June 1, 1812. At the turn of the 20th century, much of the contemporary scholarship re-evaluated this explanation and began to focus more on non-maritime factors as significant contributing causes as well. However, historian Warren H. Goodman warns that too much focus on these ideas can be equally misleading.

In disagreeing with those interpretations that have simply stressed expansionism and minimized maritime causation, historians have ignored deep-seated American fears for national security, dreams of a continent completely controlled by the republican United States, and the evidence that many Americans believed that the War of 1812 would be the occasion for the United States to achieve the long-desired annexation of Canada.Thomas Jefferson well summarized American majority opinion about the warto say "that the cession of Canadamust be a sine qua non at a treaty of peace." - Horsman

Historian Richard Maass argues that the expansionist theme is a myth that goes against the "relative consensus among experts that the primary American objective was the repeal of British maritime restrictions". He says that scholars agree that the United States went to war "because six years of economic sanctions had failed to bring Britain to the negotiating table, and threatening the Royal Navy's Canadian supply base was their last hope". Maass agrees that expansionism might have tempted Americans on a theoretical level, but he finds that "leaders feared the domestic political consequences of doing so", particularly because such expansion "focused on sparsely populated western lands rather than the more populous eastern settlements". To what extent that American leaders considered the question of pursuing territory in Canada, those questions "arose as a result of the war rather than as a driving cause." However, Maass accepts that many historians continue to believe that expansionism was a cause.

Reginald Horsman sees expansionism as a secondary cause after maritime issues, noting that many historians have mistakenly rejected expansionism as a cause for the war. He notes that it was considered key to maintaining sectional balance between free and slave states thrown off by American settlement of the Louisiana Territory and widely supported by dozens of War Hawk congressmen such as Henry Clay, Felix Grundy, John Adams Harper and Richard Mentor Johnson, who voted for war with expansion as a key aim. However, Horsman states that in his view "the desire for Canada did not cause the War of 1812" and that "The United States did not declare war because it wanted to obtain Canada, but the acquisition of Canada was viewed as a major collateral benefit of the conflict".

However, other historians believe that a desire to permanently annex Canada was a direct cause of the war.Carl Benn notes that the War Hawks' desire to annex the Canadas was similar to the enthusiasm for the annexation of Spanish Florida by inhabitants of the American South as both expected war to facilitate expansion into long-desired lands and end support for hostile tribes (Tecumseh's Confederacy in the North and the Creek in the South).

Alan Taylor says that many Democratic-Republican congressmen such as John Adams Harper, Richard Mentor Johnson and Peter Buell Porter "longed to oust the British from the continent and to annex Canada". A few Southerners opposed this, fearing an imbalance of free and slave states if Canada was annexed. Anti-Catholicism also caused many to oppose annexing the mainly Catholic Lower Canada, believing its French-speaking inhabitants unfit "for republican citizenship".

Even major figures such as Henry Clay and James Monroe expected to keep at least Upper Canada in an easy conquest. Notable American generals such as William Hull issued proclamations to Canadians during the war promising republican liberation through incorporation into the United States. General Alexander Smyth similarly declared to his troops when they invaded Canada that "you will enter a country that is to become one of the United States. You will arrive among a people who are to become your fellow-citizens". However, a lack of clarity about American intentions undercut these appeals.

David and Jeanne Heidler argue that "most historians agree that the War of 1812 was not caused by expansionism but instead reflected a real concern of American patriots to defend United States' neutral rights from the overbearing tyranny of the British Navy. That is not to say that expansionist aims would not potentially result from the war". However, they also argue otherwise, saying that "acquiring Canada would satisfy America's expansionist desires", also describing it as a key goal of western expansionists who, they argue, believed that "eliminating the British presence in Canada would best accomplish" their goal of halting British support for tribal raids. They argue that the "enduring debate" is over the relative importance of expansionism as a factor, and whether "expansionism played a greater role in causing the War of 1812 than American concern about protecting neutral maritime rights".

In the 1960s, the work of Norman K. Risjord, Reginald Horsman, Bradford Perkins and Roger Brown established a new eastern maritime consensus. While these authors approached the origins of the war from many perspectives, they all conceded that British maritime policy was the principal cause of the war.
Provide a short, bulleted summary of what historians consider the cause of the War of 1812
Different historians believe the war of 1812 was caused by: 
1. National honor, neutral maritime rights, and naval ship seizures
2. Desire by the United States to permanently annex Canada
3. British maritime policy and its perceived threat on the United States