This is going to be a surface level review of over a century of conflict, but I’ll try to do it justice.

In 1783, America and Britain signed the Treaty of Paris, ending the American Revolution. The most important parts of the treaty for us are:

Article 4: debts between private individuals in each country still needed to be repaid (looking at you, Virginian planters);

Articles 5 and 6: Loyalists who had their property seized by Americans during the war would have it returned, and not be harassed in the future; and

Article 7: “his Britanic Majesty shall with all convenient speed, and without causing any Destruction, or carrying away any Negroes or other Property of the American inhabitants, withdraw all his Armies, Garrisons & Fleets from the said United States, and from every Post, Place and Harbour within the same; leaving in all Fortifications, the American Artillery that may be therein.” (1)

From the American side, articles 4, 5 and 6 were a problem. Violence against loyalists was common during the war, and many had fled to Britain or other British colonies after having their property destroyed or seized by patriots. The British government had taken upon itself to (stingily) repay the loyalists for their lost property, either in cash or land grants in Canada, and wanted the United States to shoulder this financial burden, which it was reluctant to do. The government also had little power or desire to compel private citizens to repay their debts to someone in another country, especially one they had just been at war with.

From the British side, article 7 was the most problematic. During the war, some British commanders, most famously Lord Dunmore, had promised liberty to any slaves who left their masters and fought for the British. When the war was over, Britain kept that promise, which was in contravention of the treaty. Further, the British were reluctant to abandon key forts near the Great Lakes, citing American non-compliance with articles 4 and 5 as the reason they were not handing them over.

Although the Treaty of Paris had ended the war, the British had not consulted their indigenous allies. In the Ohio Valley, formerly British-allied tribes continued to fight the United States (the Northwest Indian War, if you are interested in looking further into this), while receiving supplies including weapons and ammunition from the British still stationed in the same forts they were supposed to abandon. It is important to note that the British were probably not encouraging attacks on the United States, although Americans certainly perceived it that way at the time. Rather, the British were unwilling to give up their alliances with the tribes of the Ohio Valley, which meant that supplies and ammunition had to continue to flow, even if British commanders in the forts disapproved of the attacks.

This would go on for another ten years, until the Jay Treaty, signed in 1795, settled most issues between Britain and America. Britain gave up the forts and gave compensation for American shipping they had raided in the meantime, America gave a lump sum to settle outstanding private debts, and both sides agreed to give each other most-favoured-nation status in trade. The treaty also established indigenous rights to cross the border unopposed, but that is not directly relevant to answering your question.

Britain was engaged in a war with France from 1793 to 1815, first against the French Revolution, then against Napoleon. Part of this war involved expanding the navy, which included the use of press gangs to force men to serve on naval vessels. However, the British took this a step further by stopping American vessels at sea, and impressing into service anyone the British officers thought was or had been a British subject, or who they identified as a deserter. This is a topic that I do not want to get too far into right now, but basically, the British argued that people born under the British crown could not give up subjecthood, even if they moved to America and gained citizenship (although the British allowed the reverse, Americans giving up citizenship to become British subjects). Anyone impressed into service who wanted to dispute the legality of their impressment could do so, but it was a long, difficult, costly, and often pointless process, settled in a British court by a British judge. Impressment had sparked outrage in the United States even before the Chesapeake-Leopard affair in 1807, where the British HMS Leopard called for the American warship USS Chesapeake to allow them to board and search for British deserters, and then fired upon the Chesapeake when it refused. Admittedly, there were British deserters onboard, but that was completely overshadowed by the fact that a British warship had fired upon and boarded an American warship.

In the Ohio Valley, Tecumseh was rallying the indigenous people into a pan-indigenous alliance, with his brother Tenskwatawa as its spiritual leader. They had founded Prophetstown in 1808, and were receiving supplies from the British, who again probably did not want a war, but did want to ensure that they would have the support of Tecumseh if there was a war, a distinction the Americans did not appreciate. Tecumseh’s efforts to rally support also helped start the Creek War further south, although American expansion into Creek territory was probably a more important factor.

Between impressment and British support of indigenous people within the United States, the decision was made to declare war on Britain in 1812; this war ended in 1815 when both sides signed the Treaty of Ghent, which essentially confirmed the status quo ante.

This would be one place to stop; it was the last war between Britain and the United States, but instead, let’s keep going to an era with genuinely good relations.

Relatively peaceful relations would be upset again in 1861, when in the middle of the American Civil War, two Confederate diplomats were discovered onboard a British ship. They had been heading to Britain to lobby for support and diplomatic recognition. How close the British were to accepting is debatable (see this post by u/petite-acorn for more detail) but the incident certainly soured relations, especially on the American side. It probably contributed to the American decision to act slowly during the Fenian raids, when the Irish Fenian Brotherhood organized small armies within the United States and invaded Canada a few times between 1866 and 1871. These had a notable lack of success, but one of those armies did contain a thousand men, and so were the cause of considerable concern within Canada.

(Part 1/2)