"The Northern Divide is not just of geographic and hydrologic importance, but it has political significance too. When the Louisiana Purchase was added to the United States in 1803, the Northern Divide served as the boundary between the territory of the United States and Great Britain (Canada). The present-day boundary between the United States and Canada was not established until 1818, when the Treaty of Ghent set the international boundary at 49º N latitude.

"The Northern Divide still has important political ramifications, because water in North Dakota drains into Canada. For example, Manitoba is citing international water laws, treaties, and compacts in its concerns over the Northwest Water Pipeline, which diverts water from the Missouri River to Minot, the proposed Garrison Diversion, which would divert Missouri River water to all of eastern North Dakota, and the planned Devils Lake outlet, which would transfer water from a closed basin to the Sheyenne/Red River system."

Information about continental divides in the United States here, at the National Atlas site.  Picture from here.