Northeast Boundary Dispute, controversy between the United States and Great Britain concerning the Maine–New Brunswick boundary. The treaty of 1783 ending the American Revolution had described the northeastern boundary of the United States as running due north from the source of the St. Croix River to the highlands dividing the St. Lawrence River tributaries and the Atlantic Ocean, and along those highlands to the northwesternmost head of the Connecticut River. Disputes over that definition lasted almost 60 years. The identity of the St. Croix was decided (1798) by a commission created by Jay's Treaty (1794). However, as no mountain range existed between the Atlantic and St. Lawrence systems, the question was submitted to arbitration, in accordance with the Treaty of Ghent (1814). The king of the Netherlands, as arbitrator, designated the St. John River as the boundary (1831), but this decision was not accepted by the United States. In 1839 the dispute led to the so-called Aroostook War, a conflict between inhabitants of New Brunswick and Maine, which produced strained relations between the United States and Great Britain. The long-standing controversy was ended with the Webster-Ashburton Treaty (1842), which set the boundary practically according to the line proposed by the king of the Netherlands, with the United States receiving the larger portion of the disputed area.
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