Washington, Treaty of, an agreement between the United States and Great Britain in 1871 that led to the settlement of various disputes between the two nations. The treaty defined the principles under which Great Britain agreed to pay damages to the United States for allowing Confederate warships to be built or outfitted in British ports during the American Civil War.
The agreement provided for determining ownership of the San Juan Islands (between Vancouver Island and United States territory). As arbiter, William I of Germany awarded the islands to the United States in 1872. They became a county of the state of Washington. The treaty also provided for free use of the St. Lawrence River by United States commercial vessels, and covered United States fishing rights in North Atlantic waters.