Venezuela Boundary Dispute, diplomatic controversy, notable for the tension caused between Great Britain and the United States during much of the 19th cent. Of long standing, the dispute concerned the boundary between Venezuela and British Guiana (now Guyana); the Venezuelan claim, extending E to the Essequibo River (and thus taking in most of the settled areas of British Guiana) had been inherited from Spain, and that of Great Britain, stretching W to the Orinoco, was acquired from the Dutch in 1810.

The controversy did not gain importance until Great Britain in 1841 had a provisional line (the Schomburgk Line) run. Discovery of gold in the region intensified the dispute. Great Britain refused to arbitrate concerning the settled area; Venezuela, however, maintained that the British were delaying in order to push settlements farther into the disputed area. Venezuela sought aid from the United States and in 1887 broke off diplomatic relations with Great Britain. President Grover Cleveland's secretary of state, Thomas Francis Bayard, began negotiations, but the matter lapsed.

In 1895, Secretary of State Olney, invoking a new and broader interpretation of the Monroe Doctrine, virtually demanded arbitration, basing the right of the United States to intercede on the ground that any state whose interests or prestige is involved in a quarrel may intervene. Lord Salisbury, the British prime minister, offered to submit some of the area to arbitration but refused to allow British settlements to be submitted to adjudication. That reply, a rebuff to Olney, brought Cleveland's momentous message to Congress on Dec. 17, 1895, which denounced British refusal to arbitrate and maintained that it was the duty of the United States to take steps to determine the boundary and to resist any British aggression beyond that line once it had been determined.

The president's message caused a commotion; Congress supported him but, although there was some war talk, neither nation desired to fight. Salisbury, involved in European troubles and disturbed by difficulties in South Africa, sent a conciliatory note recognizing the broad interpretation of the Monroe Doctrine. An American commission was appointed, and the line that was finally drawn in 1899 made an award generally favorable to Great Britain. Venezuela has periodically revived its claims to the disputed territory, most recently in 2000 under the nationalist President Hugo Chávez.

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.

Northwest Boundary Dispute: see San Juan Boundary Dispute.

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.