<span>The treaty was signed on June 15, 1846,
ending the joint occupation with Great Britain and making most
Oregonians below the 49th parallel American citizens. ... When the
Colony of British Columbia joined Canada in 1871, the 49th Parallel and
marine boundaries established by the Oregon Treaty became the Canada–US border.</span>
They wanted to find more natural resources, and they also wanted to seek out new markets for European goods.
Voting as a partisan can be an effective way to mobilize your constituents to keep voting for you, as long as you don't engage even more partisan wings of your party.
Unlike moderates or people who compromise, partisans don't have the ability to draw new members into their coalition, unless new people see their way of thinking.
South Africa is the answer