What were the cause(s) of the 1812 war?
Three excerpts from the Committee on Foreign Relations: Report on the Causes and Reasons for War, June 1812, which was an official report from the subject committee as to the causes of the war, and as an 'appeal to arms' against Great Britain:
'…After the experience which the United States have had of the great injustice of the British Government towards them, exemplified by so many acts of violence and oppression, it will be more difficult to justify to the impartial world their patient forbearance, than the measures to which it had become necessary to resort, to avenge the wrongs, and vindicate the rights and honor of the nation. Your committee are happy to observe, on a dispassionate review of the conduct of the United States, that they see in it no cause for censure.'
'…More than seven years have elapsed since the commencement of this system of hostile aggression by the British Government, on the rights and interests of the United States. The manner of its commencement was not less hostile than the spirit with which it has been prosecuted. The United States have invariably done everything in their power to preserve the relations of friendship with Great Britain…'
'…This lawless waste of our trade, and equally unlawful impressment of our seamen, have been much aggravated by the insults and indignities attending them. Under the pretext of blockading the harbors of France and her allies, British squadrons have been stationed on our own coast, to watch and annoy our own trade. To give effect to the blockade of European ports, the ports and harbors of the United States, have been blockaded. In executing these orders of the British government, or in obeying the spirit which was known to animate it, the commanders of these squadrons have encroached on our jurisdiction, seized our vessels, and carried into effect impressments within our limits, and done other acts of great injustice, violence, and oppression. The United States have seen with mingled indignation and surprise, that these acts instead of procuring to the perpetrators the punishment due to unauthorized crimes, have not failed to recommend them to the favor of the government.'
'Whether the British government has contributed by active measures to excite against us the hostility of the savage tribes on our frontiers, your committee are not disposed to occupy much time in investigating. Certain indications of general notoriety may supply the place of authentic documents, though these have not been wanting to establish the fact in some instances. It is known that symptoms of British hostility towards the United States have never failed to produce corresponding symptoms among those tribes. It is also well known that on al such occasions abundant supplies of the ordinary munitions of war have been afforded by the agents of the British commercial companies, and even from British garrisons, wherewith they were enabled, to commence that system of savage warfare on our frontiers which has been at all times indiscriminate in its effect, on all ages, sexes, and conditions and so revolting to humanity.'
So it appears that the maritime issues were causes of the war. The conquest of Canada was neither an object for declaring war nor a cause of the war itself:
Canada is not mentioned at all in Madison's 'War Message to Congress' in June 1812.
Canada is not mentioned in the US House of Representatives Committee on Foreign Relations 'Report on the Causes and Reasons for War' previously mentioned.
Canada is mentioned in a letter from Secretary of State James Monroe on 13 June 1812 to John Taylor, mentioning that 'in case of war it might be necessary to invade Canada, not as an object of the war but as a means to bring it to a satisfactory conclusion.'
So, it does seem by these three documents that the conquest of Canada was not a war aim of Madison but as a means to attack the British on land. That seems to be a common sense idea in order to take the war to the enemy and not wait on the defensive. Any idea of 'conquest' would come as an afterthought, not as an initial war aim by the Madison administration.
The War of 1812 by Harry L. Coles has some interesting discussion of the causes of the War of 1812 in the first chapter, Prologue to War, 23-25.
He notes that President Madison submitted his ‘war message' to Congress on 1 June 1812 and that ‘the document was an indictment of British policy under five main heads.'
First-impressment.
Second-‘the practice of British cruisers hovering near American ports and harassing entering and departing commerce.'
Third-‘the blockades that were…illegal even according to definitions issued by the British themselves.'
Fourth-the Orders in Council. Madison charged ‘that the commerce of the United States is to be sacrificed, not as interfering with the belligerent rights of Great Britain; not as supplying the wants of her enemies, which she herself supplies; but as interfering with the monopoly which she covets for her own commerce and navigation.' George Canning charged in parliament ‘that the Orders in Council had been transformed from a blockade into ‘a measure of commercial rivalry.' And Canning was ‘a staunch adherent of strict blockades.'
The ‘commercial rivalry' denounced by Canning ‘had been done through the sue and the abuse of a system of special licenses. The Board of Trade had the power to issue licenses exempting ships and cargoes from the effects of the blockade. It is not difficult to see that the interests of the empire might be well served by a judicious use of such power. The issue of licenses, however, became honeycombed with favoritism, corruption, and fraud. Many an Englishman who would have supported the government to the death on impressment and legitimate blockades blushed at the traffic in special licenses.'
Fifth-‘the renewal of Indian warfare on the western frontier.'
So, of Madison's five points for declaring war, four were concerned with maritime issues, and one with the Indians. There were none for invading and taking Canada as a permanent possession.
I do hope this answers the question that was put.