The “war” you’re looking for is the Pig War of 1859 , a bloodless border standoff between the United States and the United Kingdom. It began when an American settler on San Juan Island shot a British-owned pig that was eating his potatoes. The incident escalated into a serious diplomatic and military crisis over the disputed U.S.–British boundary in the San Juan Islands, with troops and warships from both sides facing off. Despite the name, no human beings were killed, and the conflict was eventually resolved peacefully through negotiation and international arbitration.