One of the more amusing stories I've come across recently in Canada/US relations has been given the rather interesting label "The Pig War". What started as a dispute over a slain pig turned into an international incident in the mid 1800s on San Juan Island.
In June 1846, the Treaty of Oregon was signed in London. This treaty established the 49th parallel as the border between the United States and what would later become Canada. The problem came from some wording that said that the US owned "...to the middle of the channel which separates the continent from Vancouver Island...". There are actually two channels, of which San Juan Island lies in the middle of; the Haro Strait, and the Rosario Strait. Depending on which side you were on, the island belonged either to the US, or to Britain.
In 1851, the Hudson's Bay Company established salmon curing stations along the coast of the island. In 1853, the island was claimed as part of the new US Washington territory. Not to be outdone, the HBC then established sheep farms. By 1859, Americans had started staking claims to the land. While they viewed it as their right, seeing as how the Americans had claimed San Juan Island, the British on the other hand viewed them as squatters.
It all came to a head on 15 June 1859. A pig owned by the HBC was shot and killed by an American man by the name of Lyman Cutlar. The pig had been rooting around in his garden. The British threatened to arrest Cutler and evict the other Americans off the island as trespassers. In response, the Americans request the help of the army. Brigadier General William S Harney was in charge of the Department of Oregan. Fiercely anti-British, he dispatched a company of the 9th US Infantry to San Juan Island. The company was under the command of Captain George E Pickett. They landed on 27 July 1859, and set up camp right near the HBC's wharf on Griffin Bay.
The actions of the Americans incensed James Douglas, the Governor of The Crown Colony of British Columbia. he responded by sending three warships. The HMS Tribune, HMS Satellite, and HMS Plumper had between them 62 guns. The instructions were to dislodge the American troops, but to avoid clashes if possible. Pickett refused to withdraw. The situation kept escalating until President James Buchanan sent General Wilfred Scott to diffuse the situation. Neither the British government nor the American government could believe that a farmer shooting a pig could have turned into almost all out war.
By mutual agreement between Douglas and Scott, the island remained under joint military occupation for 12 years. In 1871, the two governments signed the Treaty of Washington. They referred the question of ownership of San Juan Island to Kaiser Wilhelm I of Germany. On 21 October 1872, he ruled in favor of the Americans. San Juan Island became part of Washington. It also completed the final boundary between what is now Canada, and the United States.
You can read more about the war where the only casualty was an HBC pig at: