The Pig War was a confrontation in 1859 between the United States and the United Kingdom over the British–U.S. border in the San Juan Islands, between Vancouver Island (present-day Canada) and the State of Washington. The Pig War, so called because it was triggered by the shooting of a pig, is also called the Pig Episode, the Pig and Potato War, the San Juan Boundary Dispute, and the Northwestern Boundary Dispute. Despite being referred to as a "war", there were no human casualties on either side.
Background
Border ambiguity
The Oregon Treaty of June 15, 1846, resolved the Oregon boundary dispute by dividing the Oregon Country/Columbia District between the United States and Britain "along the forty-ninth parallel of north latitude to the middle of the channel which separates the continent from Vancouver Island, and thence southerly through the middle of the said channel, and of the Strait of Juan de Fuca, to the Pacific Ocean."
However, two straits could be called the middle of the channel: Haro Strait, along the west side of the San Juan Islands; and Rosario Strait, along the east side.
In 1846, there was still some uncertainty about the region's geography. The most commonly available maps were those of George Vancouver, published in 1798, and of Charles Wilkes, published in 1845. In both cases, the maps are unclear in the vicinity of the southeastern coast of Vancouver Island and the Gulf Islands. As a result, Haro Strait is not fully clear either.
In 1856, the US and Britain set up a Boundary Commission to resolve several issues regarding the international boundary, including the water boundary from the Strait of Georgia to the Strait of Juan de Fuca. The British appointed James Charles Prevost First Commissioner, George Henry Richards Second Commissioner, and William A. G. Young Secretary. The US appointed Archibald Campbell First Commissioner, John Parke Second Commissioner, and William J. Warren Secretary. On June 27, 1857, the American and British commissioners met for the first time on board the British ship HMS Satellite, anchored in Esquimalt Harbour. The two sides met several more times in 1857 in Esquimalt Harbour and Nanaimo Harbour, and corresponded by letter between meetings. The water boundary was discussed from October to December. From the start, Prevost maintained that Rosario Strait was required by the treaty's wording and was intended by the treaty framers, while Campbell had the same opinion for Haro Strait.
Prevost held that the channel specified in the treaty must have three essential qualities: it must separate the continent from Vancouver Island it must carry the boundary in a southerly direction it must be navigable
Only Rosario fulfilled these requirements, he wrote. Campbell countered that the expression "southerly", in the treaty, was to be understood in a general sense, that Rosario Strait did not separate the continent from Vancouver Island, but the San Juan Islands from Lummi Island, Cypress Island, Fidalgo Island, and others, and that navigability was not germane to the issue, but even if it was, Haro Strait was the wider and more direct passage. Finally, he challenged Prevost to produce any evidence showing that the treaty framers had intended Rosario Strait. Prevost responded to the challenge by referring to American maps showing the boundary running through Rosario Strait, including one by John C. Frémont, produced for and published by the US government, and another by John B. Preston, Surveyor General of Oregon in 1852. To the other points, Prevost repeated his statements about Rosario Strait's navigability—the channels between Lummi, Cypress, and Fidalgo islands not being navigable—and that a line through Rosario would be southerly. At the same time, one through Haro would have to be drawn westerly. The two continued to discuss the issue into December 1857, until it was clear what each side's argument was and that neither would be convinced of the other. Prevost made a final offer at the sixth meeting, on December 3. He suggested a compromise line through San Juan Channel, which would give the US all the main islands except San Juan Island. This offer was rejected and the commission adjourned, agreeing to report back to their respective governments. Thus ambiguity over the water boundary remained.
Because of this ambiguity, both the United States and Britain claimed sovereignty over the San Juan Islands. During this period of disputed sovereignty, Britain's Hudson's Bay Company established operations on San Juan and turned the island into a sheep ranch. Meanwhile, by mid-1859, twenty-five to twenty-nine American settlers had arrived.