Historians have long debated the relative weight of the multiple reasons underlying the origins of the War of 1812. This section summarizes several contributing factors which resulted in the declaration of war by the United States.
Honour and the second war of independence
As Risjord (1961) notes, a powerful motivation for the Americans was the desire to uphold national honour in the face of what they considered to be British insults such as the Chesapeake–Leopard affair. H. W. Brands says, "The other war hawks spoke of the struggle with Britain as a second war of independence; [Andrew] Jackson, who still bore scars from the first war of independence, held that view with special conviction. The approaching conflict was about violations of American rights, but it was also about vindication of American identity." Americans at the time and historians since have often called it the United States' "Second War of Independence".
The British were also offended by what they considered insults such as the Little Belt affair. This gave the British a particular interest in capturing the United States flagship President, which they succeeded in doing in 1815.
In 1807, Britain introduced a series of trade restrictions via the Orders in Council to impede neutral trade with France, which Britain was then fighting in the Napoleonic Wars. The United States contested these restrictions as illegal under international law. Historian Reginald Horsman states, "a large section of influential British opinion, both in the government and in the country, thought that America presented a threat to British maritime supremacy."
The American merchant marine had come close to doubling between 1802 and 1810, making it by far the largest neutral fleet. Britain was the largest trading partner, receiving 80% of U.S. cotton and 50% of other U.S. exports. The British public and press were resentful of the growing mercantile and commercial competition. The United States' view was that Britain's restrictions violated its right to trade with others.
During the Napoleonic Wars, the Royal Navy expanded to 176 ships of the line and 600 ships overall, requiring 140,000 sailors to man. While the Royal Navy could man its ships with volunteers in peacetime, it competed in wartime with merchant shipping and privateers for a small pool of experienced sailors and turned to impressment from ashore and foreign or domestic shipping when it could not operate its ships with volunteers alone.
The United States believed that British deserters had a right to become U.S. citizens. Britain did not recognize a right whereby a British subject could relinquish his status as a British subject, emigrate and transfer his national allegiance as a naturalized citizen to any other country. This meant that in addition to recovering naval deserters, it considered any United States citizens who were born British liable for impressment. Aggravating the situation was the reluctance of the United States to issue formal naturalization papers and the widespread use of unofficial or forged identity or protection papers by sailors. This made it difficult for the Royal Navy to distinguish Americans from non-Americans and led it to impress some Americans who had never been British. Some gained freedom on appeal. Thus while the United States recognized British-born sailors on American ships as Americans, Britain did not. It was estimated by the Admiralty that there were 11,000 naturalized sailors on United States ships in 1805. U.S. Secretary of the Treasury Albert Gallatin stated that 9,000 U.S. sailors were born in Britain. Moreover, a great number of these British born sailors were Irish. An investigation by Captain Isaac Chauncey in 1808 found that 58% of sailors based in New York City were either naturalized citizens or recent immigrants, the majority of these foreign born sailors (134 of 150) being from Britain. Moreover, 80 of the 134 British sailors were Irish.
American anger at impressment grew when British frigates were stationed just outside U.S. harbours in view of U.S. shores and searched ships for contraband and impressed men while within U.S. territorial waters. Well publicized impressment actions such as the Leander affair and the Chesapeake–Leopard affair outraged the American public.
The British public in turn were outraged by the Little Belt affair, in which a larger American ship clashed with a small British sloop, resulting in the deaths of 11 British sailors. Both sides claimed the other fired first, but the British public in particular blamed the U.S. for attacking a smaller vessel, with calls for revenge by some newspapers, while the U.S. was encouraged by the fact they had won a victory over the Royal Navy. The U.S. Navy also forcibly recruited British sailors but the British government saw impressment as commonly accepted practice and preferred to rescue British sailors from American impressment on a case-by-case basis.
British support for Native American raids
The Northwest Territory, which consisted of the modern states of Ohio, Indiana, Illinois, Michigan, and Wisconsin, was the battleground for conflict between the Native American Nations and the United States. The British Empire had ceded the area to the United States in the Treaty of Paris in 1783, both sides ignoring the fact that the land was already inhabited by various Native American nations. These included the Miami, Winnebago, Shawnee, Fox, Sauk, Kickapoo, Delaware and Wyandot. Some warriors, who had left their nations of origin, followed Tenskwatawa, the Shawnee Prophet and the brother of Tecumseh. Tenskwatawa had a vision of purifying his society by expelling the "children of the Evil Spirit": the American settlers. The Indians wanted to create their own state in the Northwest to end the American threat forever as it became clear that the Americans wanted all of the land in the Old Northwest for themselves. Tenskwatawa and Tecumseh formed a confederation of numerous tribes to block American expansion. The British saw the Native American nations as valuable allies and a buffer to its Canadian colonies and provided arms. Attacks on American settlers in the Northwest further aggravated tensions between Britain and the United States. Raiding grew more common in 1810 and 1811; Westerners in Congress found the raids intolerable and wanted them permanently ended. British policy towards the Indians of the Northwest was torn between the desire to keep the Americans fighting in the Northwest, and to preserve a region that provided rich profits for Canadian fur traders, versus the fear that too much support for the Indians would cause a war with the United States. Through Tecumseh's plans for an Indian state in the Northwest would benefit British North America by making it more defensible, at the same time, the defeats suffered by Tecumseh's confederation had the British leery of going too far to support what was probably a losing cause. In the months running up to the war, British diplomats attempted to defuse tensions on the frontier.
The confederation's raids, and its very existence, hindered American expansion into rich farmlands in the Northwest Territory. Pratt writes:
There is ample proof that the British authorities did all in their power to hold or win the allegiance of the Indians of the Northwest with the expectation of using them as allies in the event of war. Indian allegiance could be held only by gifts, and to an Indian no gift was as acceptable as a lethal weapon. Guns and ammunition, tomahawks and scalping knives were dealt out with some liberality by British agents.
However, according to the U.S. Army Center of Military History, the "land-hungry frontiersmen", with "no doubt that their troubles with the Native Americans were the result of British intrigue", exacerbated the problem by "[circulating stories] after every Native American raid of British Army muskets and equipment being found on the field". Thus, "the westerners were convinced that their problems could best be solved by forcing the British out of Canada".
The British had the long-standing goal of creating a large, "neutral" Native American state to cover much of Ohio, Indiana, and Michigan. They made the demand as late as the fall of 1814 at the peace conference, but lost control of western Ontario in 1813 at key battles on and around Lake Erie. These battles destroyed the Indian confederacy which had been the main ally of the British in that region, weakening its negotiating position. Although much of the area remained under British or British-allied Native Americans' control until the end of the war, the British, at American insistence and with higher priorities, dropped the demands.
American expansion into the Northwest Territory was being obstructed by various Indian tribes since the end of the Revolution, who were supplied and encouraged by the British. Americans on the western frontier demanded that interference be stopped. There is dispute, however, over whether or not the American desire to annex Canada brought on the war. Several historians believe that the capture of Canada was intended only as a means to secure a bargaining chip, which would then be used to force Britain to back down on the maritime issues. It would also cut off food supplies for Britain's West Indian colonies, and temporarily prevent the British from continuing to arm the Indians. However, many historians believe that a desire to annex Canada was a cause of the war. This view was more prevalent before 1940, but remains widely held today. Congressman Richard Mentor Johnson told Congress that the constant Indian atrocities along the Wabash River in Indiana were enabled by supplies from Canada and were proof that "the war has already commenced. ... I shall never die contented until I see England's expulsion from North America and her territories incorporated into the United States."
Madison believed that British economic policies designed to foster imperial preference were harming the American economy and that as British North America existed, here was a conduit for American strugglers who were undercutting his trade policies, which thus required that the United States annex British North America. Furthermore, Madison believed that the Great Lakes-St. Lawrence trade route might become the main trade route for the export of North American goods to Europe at the expense of the U.S. economy, and if the United States controlled the resources of British North America like timber which the British needed for their navy, then Britain would be forced to change its maritime policies which had so offended American public opinion. Many Americans believed it was only natural that their country should swallow up North America with one Congressman, John Harper saying in a speech that "the Author of Nature Himself had marked our limits in the south, by the Gulf of Mexico and on the north, by the regions of eternal frost". Upper Canada (modern southern Ontario) had been settled mostly by Revolution-era exiles from the United States (United Empire Loyalists) or postwar American immigrants. The Loyalists were hostile to union with the United States, while the immigrant settlers were generally uninterested in politics and remained neutral or supported the British during the war. The Canadian colonies were thinly populated and only lightly defended by the British Army. Americans then believed that many men in Upper Canada would rise up and greet an American invading army as liberators. That did not happen. One reason American forces retreated after one successful battle inside Canada was that they could not obtain supplies from the locals. But the Americans thought that the possibility of local support suggested an easy conquest, as former President Thomas Jefferson believed: "The acquisition of Canada this year, as far as the neighborhood of Quebec, will be a mere matter of marching, and will give us the experience for the attack on Halifax, the next and final expulsion of England from the American continent."
Annexation was supported by American border businessmen who wanted to gain control of Great Lakes trade.
Carl Benn noted 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; both expected war to facilitate expansion into long-desired lands and end support for hostile Indian tribes (Tecumseh's Confederacy in the North and the Creek in the South).
Tennessee Congressman Felix Grundy considered it essential to acquire Canada to preserve domestic political balance, arguing that annexing Canada would maintain the free state-slave state balance, which might otherwise be thrown off by the acquisition of Florida and the settlement of the southern areas of the new Louisiana Purchase.
Historian Richard Maass argued in 2015 that the expansionist theme is a myth that goes against the "relative consensus among experts that the primary U.S. objective was the repeal of British maritime restrictions". He argues that consensus among scholars is 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 theoretically expansionism might have tempted Americans, but finds that "leaders feared the domestic political consequences of doing so. Notably, what limited expansionism there was focused on sparsely populated western lands rather than the more populous eastern settlements [of Canada]." Nevertheless, Maas notes that many historians continue to believe that expansionism was a cause.
Horsman argued expansionism played a role 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 John A. Harper, Felix Grundy, Henry Clay, and Richard M. Johnson, who voted for war with expansion as a key aim.
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 war ... to say "that the cession of Canada ... must be a sine qua non at a treaty of peace".
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."
Historian Alan Taylor says that many Democratic-Republican congressmen, such as Richard M. Johnson, John A. Harper and Peter B. 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, while anti-Catholicism also caused many to oppose annexing 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 the event of an easy conquest. Notable American generals, like William Hull were led by this sentiment to issue proclamations to Canadians during the war promising republican liberation through incorporation into the United States; a proclamation the government never officially disavowed. General Alexander Smyth similarly declared to his troops that when they invaded Canada "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." A lack of clarity about American intentions undercut these appeals, however.
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 Indian 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."
U.S. political conflict
While the British government was largely oblivious to the deteriorating North American situation because of its involvement in a continent-wide European war, the U.S. was in a period of significant political conflict between the Federalist Party (based mainly in the Northeast), which favoured a strong central government and closer ties to Britain, and the Democratic-Republican Party (with its greatest power base in the South and West), which favoured a weak central government, preservation of states' rights (including slavery), expansion into Indian land, and a stronger break with Britain. By 1812, the Federalist Party had weakened considerably, and the Republicans, with James Madison completing his first term of office and control of Congress, were in a strong position to pursue their more aggressive agenda against Britain. Throughout the war, support for the U.S. cause was weak (or sometimes non-existent) in Federalist areas of the Northeast. Few men volunteered to serve; the banks avoided financing the war. The negativism of the Federalists, especially as exemplified by the Hartford Convention of 1814–15, ruined its reputation and the Party survived only in scattered areas. By 1815 there was broad support for the war from all parts of the country. This allowed the triumphant Democratic-Republicans to adopt some Federalist policies, such as a national bank, which Madison reestablished in 1816.