After the French and Indian War, Britain's trans-Appalachian Indian Reserve was divided by the river into colonial lands to the south and Native American lands to the north. In the late 18th century, the river became the southern boundary of the Northwest Territory. The river is sometimes considered as the western extension of the Mason–Dixon line that divided Pennsylvania from Maryland, and thus part of the border between free and slave territory, and between the Northern and Southern United States or Upper South. Where the river was narrow, it was crossed by thousands of slaves escaping to the North for freedom; many were helped by free blacks and whites of the Underground Railroad resistance movement.
After the French and In.dian War, Britain's trans-Appalachian Indian Reserve was divided by the river into colonial lands to the south and Native American lands to the north In the late 18th century, the river became the southern boundary of the Northwest Territ.ory. The river is sometimes considered as the western extension of the Mason–Dixon line that divided Pennsylvania from Maryland, and thus part of the border between free and slave territory, and between the Northern and Southern United States or Upper South. Where the river was narrow, it was crossed by thousands of slaves escaping to the North for freedom; many were helped by free blacks and whites of the Underground Railroad resistance movement