Which 1846 treaty settled the Oregon boundary dispute between the US and Britain?

The Oregon Treaty, which put the border at the 49th parallel and ended a dispute that had produced one of the great political slogans: fifty-four forty or fight, meaning the Americans should demand everything up to latitude 54 degrees 40 minutes and go to war if refused.

They did not. Polk campaigned on the maximum claim and then settled for roughly half of it, because the United States was about to start a war with Mexico and had no appetite for a second one with the Royal Navy. The compromise gave Britain what became British Columbia and gave the Americans the Columbia River basin and Puget Sound.

The line has one deliberate kink. Running the parallel straight out to sea would have cut Vancouver Island in two, so the boundary swings south around it - which left ownership of the San Juan Islands ambiguous. That produced the Pig War of 1859, in which an American shot a British pig eating his potatoes, both sides landed troops, and the only casualty in twelve years of joint military occupation was the pig.