The Oregon Treaty of 1846 had established the border between American and British territory in the Pacific Northwest at the 49th parallel 'to the middle of the channel which separates the continent from Vancouver's Island.' The problem was, there were multiple channels. Both countries claimed the San Juan Islands, which sat between them.

By 1859, both American and British settlers occupied San Juan Island. The Americans were mostly farmers. The British presence was primarily the Hudson's Bay Company, which ran sheep on the island. The two communities coexisted uneasily, each claiming their country owned the island.

Lyman Cutlar was an American farmer who had been growing potatoes on San Juan Island. On June 15, 1859, he found a large black pig rooting in his garden - not for the first time. He shot the pig. The pig, it turned out, belonged to the Hudson's Bay Company and was valued at $10 by its owner (who had previously valued it at $10 when Cutlar offered to buy it, then raised the price to $100 after it was dead).

The incident might have ended with a payment, but tempers flared. Cutlar allegedly told the pig's owner, 'It was eating my potatoes.' The owner allegedly replied, 'It is up to you to keep your potatoes out of my pig.' British authorities threatened to arrest Cutlar. American settlers demanded military protection.

The U.S. Army responded by sending 66 soldiers under Captain George Pickett (who would later lead the famous charge at Gettysburg). The British responded by sending warships. Pickett's commander, Brigadier General William Harney, sent reinforcements. The British sent more ships. By August, 461 American soldiers with 14 cannons faced five British warships with 167 guns and over 2,000 men.

Rear Admiral Robert Baynes, commanding the British forces, refused orders to land marines and engage the Americans. 'Two great nations in a war over a squabble about a pig,' he reportedly said. The standoff continued, but no shots were fired.

Cooler heads eventually prevailed. American General Winfield Scott arrived to negotiate a de-escalation. Both sides agreed to a joint military occupation of the island - American troops at one end, British at the other - while diplomats worked out a solution.

The joint occupation lasted twelve years. American and British soldiers shared the island peacefully, even celebrating each other's holidays. The American camp flew the British flag on Queen Victoria's birthday; the British camp flew the American flag on July 4th. The pig was the only casualty of the Pig War.

In 1871, the United States and Britain agreed to submit the border dispute to international arbitration. Kaiser Wilhelm I of Germany was chosen as arbitrator. On October 21, 1872, the Kaiser ruled in favor of the United States. The San Juan Islands became American territory.

British troops withdrew in November 1872, ending thirteen years of joint occupation. The pig was never replaced. Lyman Cutlar faded into obscurity. Today, San Juan Island National Historical Park preserves both the American and British camps. The Pig War remains the only armed conflict between the United States and Great Britain since the War of 1812 - and the only one to end without a human casualty.