To the Senate of the United States:
The treaty concluded between Great Britain and the United States on the 15th of June, 1846, provided in its first article that the line of boundary between the territories of Her Britannic Majesty and those of the United States from the point on the forty-ninth parallel of north latitude up to which it had already been ascertained should be continued westward along the said parallel "to the middle of the channel which separates the continent from Vancouvers Island, and thence southerly through the middle of said channel and of Fucas Straits to the Pacific Ocean." When the commissioners appointed by the two Governments to mark the boundary line came to that point of it which is required to run southerly through the channel which divides the continent from Vancouvers Island, they differed entirely in their opinions, not only concerning the true point of deflection from the forty-ninth parallel, but also as to the channel intended to be designated in the treaty. After a long-continued and very able discussion of the subject, which produced no result, they reported their disagreement to their respective Governments. Since that time the two Governments, through their ministers here and at London, have had a voluminous correspondence on the point in controversy, each sustaining the view of its own commissioner and neither yielding in any degree to the claims of the other. In the meantime the unsettled condition of this affair has produced some serious local disturbances, and on one occasion at least has threatened to destroy the harmonious relations existing between Great Britain and the United States. The island of San Juan will fall to the United States if our construction of the treaty be right, while if the British interpretation be adopted it will be on their side of the line. That island is an important possession to this country, and valuable for agricultural as well as military purposes. I am convinced that it is ours by the treaty fairly and impartially construed. But argument has been exhausted on both sides without increasing the probability of final adjustment. On the contrary, each party seems now to be more convinced than at first of the justice of its own demands. There is but one mode left of settling the dispute, and that is by submitting it to the arbitration of some friendly and impartial power. Unless this be done, the two countries are exposed to the constant danger of a collision which may end in war.
It is under these circumstances that the British Government, through its minister here, has proposed the reference of the matter in controversy to the King of Sweden and Norway, the King of the Netherlands, or to the Republic of the Swiss Confederation. Before accepting this proposition I have thought it right to take the advice of the Senate.
The precise questions which I submit are these: Will the Senate approve a treaty referring to either of the sovereign powers above named the dispute now existing between the Governments of the United States and Great Britain concerning the boundary line between Vancouvers Island and the American continent? In case the referee shall find himself unable to decide where the line is by the description of it in the treaty of 15th June, 1846, shall he be authorized to establish a line according to the treaty as nearly as possible? Which of the three powers named by Great Britain as an arbiter shall be chosen by the United States?
All important papers bearing on the questions are herewith communicated in the originals. Their return to the Department of State is requested when the Senate shall have disposed of the subject.
James Buchanan, Special Message Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/202123