Britain and the United States had made competing territorial claims in the Pacific Northwest, including much larger areas than either ultimately received. Their settlement on the 49th parallel left Canada with access to the Pacific coast. The boundary dispute also connects to the Pig War and Royal Navy officers who served in the region. If fighting resumed, British forces could threaten Oregon and try to reopen the settlement, forcing the Union to divert attention far from the main Civil War theatres.
Notable Point · 1:34-2:41
The Oregon boundary dispute in the background
An earlier Anglo-American border dispute helps explain why the Pacific coast remains relevant in a wider war scenario.