The French colors were lowered and the American flag raised in New Orleans on this date in 1803, signifying the transfer of sovereignty of Louisiana from France to the United States. Arguably the transfer was one of the two or three most defining moments in American history.
As ultimately defined, Louisiana Territory included most of the U.S. west of the Mississippi River, east of the Rocky Mountains, except for Texas and New Mexico; that is, parts or all of Louisiana, Arkansas, Missouri, Iowa, Minnesota, Oklahoma, Kansas, Nebraska, South Dakota, North Dakota, Colorado, Wyoming and Montana.