The Pig War was a real-life confrontation in 1859 between the United States and the British Empire over the boundary between the US and British North America. The territory in dispute was the San Juan Islands, which lie between Vancouver Island and the North American mainland, in what is now Washington State. The Pig War, so called because it was triggered by the shooting of a pig, is also called the Pig Episode, the Pig and Potato War, the San Juan Boundary Dispute or the Northwestern Boundary Dispute. With no human casualties, this dispute was a bloodless conflict.
According to the episode "The Pig War", the Brits and the Americans fought for control over Elk Island (likely based on Washington's real-life Skagit Island), and the event is annually reenacted in Hillwood. Though the Pig War took place on Elk/Skagit Island in the show, in real-life it took place on the San Juan Islands, 23 miles west of Skagit Island. According to Steely Phil in Hey Arnold!: The Movie, the Americans gained territorial control of Hillwood at some point after the Pig War.