‘The Pig War’ is perhaps one of the most obscure and unusual 'nearly' wars in history.
In 1859, the U.S. almost went to war with Canada because of a pig. Just a few years after the Oregon Treaty was signed to end a border dispute between America and Britain (which still ruled over the area that came to be known as Canada), things got a little heated on San Juan Island where citizens from both countries were located.
The Oregon Treaty stated that the US / British American border be drawn at the 49th parallel, a division which remains to this day. Although this all sounds rather straightforward, the situation because slightly more complicated when it came to a set of islands situated to the south-west of Vancouver.
According to Historic UK "a pig belonging to the British accidentally wandered onto the land of Lyman Cutlar, an American farmer. When Cutlar noticed the pig eating some of his potatoes he was incensed, and in a fit of rage shot and killed the pig."
Despite efforts to resolve the situation between the two men, things spread into the rest of the community and got to the point where the governor of British Columbia sent three warships to the area. The two sides continued to increase their military force over the following month until British Navy Admiral Robert L. Baynes arrived and ended things by stating that he would not "involve two great nations in a war over a squabble about a pig."