San Juan Boundary Dispute, controversy between the United States and Great Britain over the U.S.–British Columbia boundary. It is sometimes called the Northwest Boundary Dispute. The difficulty arose from the faulty wording of the treaty of 1846 that established the northern boundary of the Oregon Territory. That instrument set the boundary as a line through the middle of the channel between the mainland and Vancouver Island and through the middle of Juan de Fuca Strait. The strait, however, breaks into several channels, and between the two main ones—Haro Strait and Rosario Strait—lie the San Juan Islands. Ownership of the islands, especially San Juan Island, was disputed. The quarrel, unsettled by diplomatic negotiations, was brought to a crisis in 1859, when George E. Pickett and U.S. troops occupied San Juan Island. British war vessels promptly appeared. No armed conflict resulted because Gen. Winfield Scott, commander in chief of American armies, went to the scene and arranged with the British for joint occupation of San Juan. Until 1872 there were soldiers of both powers on the island. Attempts to appoint a neutral arbitrator were defeated by the U.S. Senate until the Washington Treaty of 1871. Emperor William I of Germany, as arbitrator in 1872, decided upon Haro Strait as the line, thus giving the San Juan archipelago to the United States.