None of this was empty country. People have lived in these islands for roughly eleven thousand years, since the continental ice sheet withdrew at the end of the last glaciation, and the six central Coast Salish nations descend from them. Archaeological evidence places hunting and gathering here six to eight thousand years ago, and shell middens lie under the ground at both American Camp and English Camp, which means both armies pitched their tents on top of villages. Smallpox arrived with European contact in the 1770s and killed people here in numbers the record can only estimate. By the time Britain and the United States began arguing over who owned the island, the population that had actually occupied it longest had already been devastated by a disease neither country brought deliberately and neither did much about.

The American homesteaders asked for military protection after the Cutlar affair and got it, which is how a dispute over livestock became an international incident. Pickett landed his infantry at the island's southern end. The British answered with Royal Navy ships, and the officer commanding them had orders that, if executed literally, would have started a war. He did not execute them literally. That refusal, repeated on both sides by men who understood what was at stake and what was not, is the actual story of the Pig War. Cooler heads arranged a joint military occupation: both nations would keep a camp on San Juan Island until diplomacy could sort out the boundary. Nobody expected that arrangement to last more than a season.

It lasted from 1859 to 1872. British Royal Marines held a camp on the island's northwest shore from 1860, in a sheltered cove with a formal garden and a blockhouse, while the American garrison occupied a wind-scoured prairie above the Strait of Juan de Fuca. The two sides built a road between them. They visited each other. The Americans in San Juan village did business with both camps, which was excellent for the village. Among the American officers was Henry Martyn Robert, a young engineer who would later write Robert's Rules of Order, the manual that governs how committees argue without descending into chaos. It is difficult to imagine a better apprenticeship for that particular book than twelve years of armed men agreeing not to shoot.

The 1871 Treaty of Washington finally handed the question to a neutral party, and the neutral party was Kaiser Wilhelm I of Germany. He considered the two competing channels and in 1872 ruled that the boundary ran through Haro Strait, the western channel, which put the San Juan Islands in the United States. The British struck their camp and left. Both sites were designated a National Historic Landmark in 1961, and on 9 September 1966 President Lyndon Johnson signed the law creating San Juan Island National Historical Park to preserve them together, an American park that exists to commemorate a dispute with Britain that both countries chose not to win by force.

The prairie at American Camp turns out to be doing something no other place on earth is doing. It holds the world's only viable population of the island marble butterfly, a small pale insect considered extinct for ninety years until it was rediscovered in 1998 and listed as endangered in 2020. Foxes hunt rabbits across the same grass. Bald eagles, northern harriers, ospreys, great horned owls, harlequin ducks and goldfinches work the park's edges, and orca, humpback and gray whales pass offshore. Trails climb Mount Finlayson at American Camp and Young Hill at English Camp, with Bell Point and the Mitchell Hill network below. South Beach opens onto the Strait of Juan de Fuca with the Olympic Mountains filling the southern horizon, and Fourth of July Beach faces the calmer water of Griffin Bay, named for the man whose pig started all of it.