In the early 1800s, several nations set out to explore what we now call the Pacific Northwest, and to take possession of those lands, despite the fact that the area was already populated by natives. In 1846, a line was drawn between the claims of Britain and the claims of the United States along the 49th parallel, except for a small part that followed "the middle of the channel which separates the continent from Vancouver Island and thence southerly through the middle of the said channel.” The could be interpreted in more than one way, and between those two interpretations lay the island of San Juan. The British sent sheep to the island. The Americans sent a tax collector to bill the shepherd, Charles Griffin. The British refused to pay. The Americans sold the sheep for taxes owed.
For the next few years, tensions on the island stayed low, as Griffin oversaw the growth of the farm to close to 4,500 sheep, along with pigs and other animals. But in 1859 American settlers started arriving, intent on setting up their own farms. One brought 20 cattle. These newcomers did not take much stock in Griffin’s presence there. One new farm was located smack in the middle of one of Griffin’s best sheep runs.
Despite their best efforts, the humans on the island had managed to avoid direct conflict, but the animals were less discreet. In summer 1859, one of the pigs from Griffin’s farm discovered a plot of tempting tubers on the farm of American Lyman Cutlar and availed himself of the delights. Cutlar, having fended off this same pig before, could not stand for this theft. He shot the pig.
An argument broke out over the value of the pig, and before you know it, the American Army and the British Navy were facing off at San Juan Island. Read how the conflict played out at Atlas Obscura.