The United States and Britain have been adversaries at war, officially, twice: the American Revolution and the War of 1812. In more modern times, the two nations have been allies. But for a few months in 1859, the two sides were again hostile, meeting each other in the field of battle, with over 400 American soldiers (and roughly a dozen cannons) facing off against more than 2,000 British troops — and five British warships.

The good news: the total casualty count from the war was one — one pig, that is.

After the War of 1812, most of the Pacific Northwest (here’s a map) was jointly occupied by both the U.S. and the United Kingdom. Over time, the two nations came to an agreement — the Oregon Treaty — which divided the territory at the 49th Parallel, forming the modern border between the state of Washington (U.S.) and the province of British Columbia (Canada). An exception was made for Vancouver Island, which was placed entirely under British control even though it dipped below the 49th Parallel. The Oregon Treaty specifically drew the line of demarcation separating the two as “the middle of the channel which separates the continent from Vancouver Island.”

The problem?

The San Juan Islands, pictured, are in the middle of that unnamed “channel,” and create three separate “middle” channels. For a dozen years after signing the Oregon Treaty, neither side particularly liked the other’s interpretation of which channel was the true divider. The U.S. preferred the Haro Strait, the blue line pictured in the map, right; the U.K. preferred the Rosario Strait, denoted by the red line. And this question of ownership causes practical problems: The British Hudson Bay Company set up a sheep ranch on San Juan Island while a few dozen Americans settled there as well.

On June 15, 1859 — thirteen years to the day that the two nations signed the Oregon Treaty — an American farmer named Lyman Cutlar noticed a pig, owned by Charles Griffin, an employee of the Hudson Bay Company, eating one of his potato crops. Cutlar considered the pig a trespasser and, angered — this was not the first time this had happened — he shot the pig. Cutlar offered Griffin $10 in compensation; Griffin demanded $100. Cutlar withdrew his offer, now believing he was fully within his rights to shoot the (trespassing) pig. Griffin called upon the British authorities to arrest Cutlar. Cutlar and other American settlers, in turn, requested that the American military protect them from the British. Things quickly spiraled out of hand and, within two months, the forces described above camped on and around San Juan Island, both with strict orders not to fire the first shot. (Opposing troops did, however, toss insults, hoping to coax the other into violating this order.)

Things came to a head when word of the conflict reached Washington, D.C. and London. Both sides wished to keep this conflict bloodless, and agreed to jointly occupy San Juan Island peacefully, each with a military base on the island. In 1874, a panel of international arbitrators declared the Haro Strait to be the border, and awarded San Juan Island to the United States; the British closed up their base soon thereafter.

Bonus fact : The military bases now, combined, make up San Juan Island National Historic Park. Pictured here, it is the only U.S. national park that commemorates a British base, and the only one where a British flag flies.

From the Archives: The World’s Shortest War: From start to finish in under an hour.

Related: “The Pig War: The Most Perfect War in History” by E. C. Coleman.