In the mid-1790s, the eastern boundary of the vast region then known as Louisiana ran along the Mississippi River from the settlement and port of New Orleans in the South to what is now the border of Canada. Louisiana's western boundary was not well defined but extended from New Orleans northwest through present-day northern Texas to the Rocky Mountains and then northward along the Rockies to Canada. Louisiana included more than 800,000 square miles. With the Treaty of Fontainebleau in 1762, France ceded, or formally surrendered, Louisiana to Spain.

At the end of the American Revolution in 1783, the United States and Britain signed the Treaty of Paris. In the treaty, Britain granted independence to the United States; Britain also granted to the United States all land west of the original colonies to the Mississippi River. The new nation stretched north to Canada (a...