Dictionary.net

In negotiating the treaty of 1846, by which the forty-ninth parallel, from the Rocky Mountains to the sea, was made the boundary between the American and British possessions, a controversy arose concerning the course of the line through the channel which divides Vancouver Island from the mainland. The Americans contended for the Canal de Haro, the British for the Rosario Strait. To avoid conflict, it was decided that both nations occupy the island of San Juan at opposite ends. In 1872 the German Emperor, acting as arbitrator, decided for America.