The Treaty of San Lorenzo
As it appears in The Laws of the United States, (Pinckney's Treaty) Folwell's, Philadelphia, 1796.
Often glossed over if not overlooked in many history books, The Treaty of San Lorenzo between Spain and the United States played a major role in the expansion of the infant nation's boundaries. Preceded by the acquisition of lands set forth by the Northwest Ordinance eight years earlier, and soon-to-be followed by the Louisiana Purchase eight years later, the Treaty of San Lorenzo (also known as Pinckney's Treaty) opened up the Mississippi River to American navigation.
Negotiated by Thomas Pinckney, America's special envoy to Spain, the agreement also allowed western settlers the "right to deposit" their exports in New Orleans and to engage in commercial transactions within that city. This was of vital importance to the more than 100,000 westerners who lived in Kentucky and Tennessee, and to the many thousands of settlers who lived in what is now Ohio. Under the treaty Spain officially recognized the southern and western boundaries of the U.S. as the 31st parallel and the Mississippi River. The treaty thus allowed the U.S. to gain access to the area now known as the states of Mississippi and Alabama.
The treaty was signed at San Lorenzo El Real on October 27, 1795.