The United States claims from the British safe passage between three pieces of land: at the mouth of the Chicago River and Lake Michigan, at Peoria, and at the mouth of the Illinois River joining the Mississippi. After the Louisiana Purchase in 1803, Congress issues a directive to appropriate a 20 mile tract of land and secure control over the trade route. Over decades or wars and treaty-making, US expansion pushes across the continental divide. John Sullivan surveyed the Indian boundary Lines first established in the Treaty of St Louis in 1816. Between these lines, the corridor emerges.