When US Secretary of State William H. Seward negotiated the purchase of Alaska from Imperial Russia in 1867 for $7. 2 million, the treaty relied heavily on language borrowed from an 1825 Anglo-Russian convention.
However, this historical copy-paste job contained a major geographical ambiguity regarding the southern boundary of Alaska through the Dixon Entrance, a strait separating Alaska's Alexander Archipelago from British Columbia's Haida Gwaii. The treaty defined the border as a line running 'along the parallel of 54 degrees 40 minutes north latitude' from the southernmost point of Prince of Wales Island eastward. The fundamental loophole emerged from whether this line—known as the 'A-B Line'—represented an absolute maritime border assigning all waters north of it to the United States, or merely a land-demarcation reference line identifying which islands belonged to whom.
Canada, inheriting Great Britain's claims, argued that international maritime law dictates a median line through the strait, giving both nations equal access to fishing and seabed rights. Conversely, the United States maintained that the 1903 Alaska Boundary Tribunal permanently established the A-B Line as an official maritime boundary, granting the US exclusive sovereignty over the northern half of the sound. Because the 1867 treaty failed to explicitly clarify water rights versus land rights, the Dixon Entrance remains one of North America's unresolved maritime border disputes, impacting commercial salmon fishing, subsea resources, and naval navigation rights.