Why does Minnesota have the Northwest Angle?

Answer 1

An important component of the the Treaty of Paris between the U.S. and Great Britain after the Revolutionary War was its defining of the northern boundary of the new United States, westward to the Mississippi River. It's language defined the western-most part of that border as running "...through the Lake of the Woods to the northwestern most point thereof, and from thence on a due west course to the river Mississippi..." The problem, however, was the incorrect assumption at the time (as illustrated on some significant maps of the day) that the Mississippi extended that far north and west, versus its source being Lake Itasca in north central Minnesota, approximately a hundred miles south of Lake of the Woods.

After the Louisiana Purchase from France in 1803, the U.S. owned substantial land west of the Mississippi, and the Convention of 1818 (or Treaty of 1818) in part established the northern border for that new U.S. territory. The U.S. and the British agreed to define the new border, from where the old one left off (at the northwestern most point of Lake of the Woods), as the 49th parallel, west to the Rocky Mountains.

Thus, that sudden drop in the border along the western edge of Lake of the Wood can simply be thought of as a correction line, one that connects the old border to the east, as defined by the Treaty of Paris in 1783, to the new border along the 49th parallel to the west, as defined by the Treaty of 1818 - thereby creating the "notch" at the top of state. Minnesota's Northwest Angle then is that section of land separated by water from the rest of the state/country but still within the borders dictated by the combination of those two treaties.