Most historians have found there is no single cause for the War of 1812 but several related causes.
In Europe, Britain, the naval power, and France, the land power, were at war with each other. Each side was trying to cripple the other’s economy with blockades and confiscation of trade goods. And the United States was trying to remain neutral. Britain issued Orders-in-Council, treating as an enemy any vessel that tried to enter a French port without first stopping at a British port to pay a fee and get a licence. The British felt this was necessary in order to defeat Napoleon, but the Americans felt Britain was insisting they should have no trade of their own and that she should control all their foreign commerce; they felt their independence was at stake.
The United States retaliated with the Embargo Act, which stopped all United States merchant vessels from sailing from United States ports and forbade commerce with any foreign nation.
The Embargo adversely affected all regions of the United States, resulting in a depression that all but paralyzed the economy of the United States. Smuggling along the Canadian border flourished.
Impressment was the most volatile issue between the United States and Britain. This was because it dealt with sovereignty. Impressment involved the right to search commercial ships for deserters. Poor food, hard work, and harsh discipline caused British sailors to desert by the thousands. Most of them ended up in America. Britain never claimed the right to search vessels of the United States Navy. She did claim the right to search private vessels as she felt this involved no invasion of another nation's sovereignty. Americans considered this to be an insult to their sovereignty.
On June 22, 1807, a vessel of the United States Navy named the Chesapeake set sail from Norfolk. The British boarded and removed four members of the Chesapeake crew who they claimed to be British deserters.
The division of land after the Revolution did not leave everyone satisfied. The loss of the Ohio River valley, housing vital fur trade routes, displeased Canadian and British merchants. It also served home to a large Indigenous population, a large part of which had supported the British during the American Revolution and now argued for an an autonomous Indigenous state to be created south and west of Lake Erie.
The Americans felt that British support of the First Nations was a threat to their expansion and their policy of forcing the conversion of First Nations peoples to farmers, giving up their hunting lands for American use.
The primary cause for the call to invade Canada was the perceived support the British in Canada were giving the Natives of the Northwest. The Americans did not miss that Canada was Britain's last foothold on the continent either. As relations with Britain worsened, the call for expansion both north and south increased in volume and frequency. The exhaustion of the farm lands in the Old Northwest caused land-hungry farmers to call for the conquest of Canada with its good lands.
All these issues resulted in the surfacing of a small yet persuasive political faction known as the War Hawks, led by Henry Clay of Kentucky, who was elected to Congress in 1810. The War Hawks demanded war with Britain.
By the time representatives of both sides of the war had arrived in the Belgian town of Ghent in August of 1814, most of the issues that had caused the war had been resolved.
The U.S. grievance, the Orders-in-Council forbidding trade with European countries, had long since been repealed by Britain; indeed, Orders-in-Council had been repealed by the end of June, 1812.
U.S. dropped the impressment issue. With Napoleon defeated, Britain had a surplus of sailors and no longer engaged in the practice.
As the peacemakers sat in Ghent in 1814, only the territorial issues remained. Once Britain agreed to drop the creation of a First Nations barrier-state between the U.S. and Canada, it was only a matter of time before both countries agreed to end hostilities by returning to the exact same conditions that had existed before the war.
On Christmas Eve of 1814, the peace treaty was signed and sealed. The eleven articles stated that the U.S. and Britain would return to the status quo ante bellum, or the exact same state of affairs as before the war. There was no mention of impressment or the Orders-in-Council; the issues which had spurred the U.S. into declaring war. On paper, it was as if the war had never been fought.