Robert Cavelier de La Salle discovers the mouth of the Mississippi River, claims it for France and names it Louisiana.

René-Robert Cavelier, Sieur de La Salle, was a 17th-century French explorer and fur trader in North America. He explored the Great Lakes region of the United States and Canada, and the Mississippi River. He is best known for an early 1682 expedition in which he canoed the lower Mississippi River from the mouth of the Illinois River to the Gulf of Mexico; there, on April 9, 1682, he claimed the Mississippi River basin for France after giving it the name La Louisiane, in honor of Saint Louis and Louis XIV. One source states that "he acquired for France the most fertile half of the North American continent". A later, ill-fated expedition in 1687 to the Gulf coast of Mexico gave the United States a putative claim to Texas in the purchase of the Louisiana Territory from France in 1803; La Salle was assassinated during that expedition.

The Mississippi River is the primary river of the largest drainage basin in the United States. It is the second-longest river in the United States, behind only the Missouri. From its traditional source of Lake Itasca in northern Minnesota, it flows generally south for 2,340 mi (3,770 km) to the Mississippi River Delta in the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains all or parts of 32 U.S. states and two Canadian provinces between the Rocky and Appalachian mountains. The river either borders or passes through the states of Minnesota, Wisconsin, Iowa, Illinois, Missouri, Kentucky, Tennessee, Arkansas, Mississippi, and Louisiana. The main stem is entirely within the United States; the total drainage basin is 1,151,000 sq mi (2,980,000 km²), of which only about one percent is in Canada. The Mississippi ranks as the world's tenth-largest river by discharge flow, and the largest in North America.

Louisiana, also known as French Louisiana, was a district of New France. In 1682, the French explorer René-Robert Cavelier, Sieur de la Salle erected a cross near the mouth of the Mississippi River and claimed the whole of the drainage basin of the Mississippi River in the name of King Louis XIV, naming it "Louisiana". This land area stretched from near the Great Lakes to the Gulf of Mexico and from the Appalachian Mountains to the Rocky Mountains. The area was under French control from 1682 to 1762 and in part from 1801 (nominally) to 1803.