Colonial history of the United States Lower Louisiana. This vast tract was first settled at Mobile and Biloxi around 1700, and continued to grow when 7,000 French immigrants founded New Orleans in 1718. Settlement proceeded very slowly; New Orleans became an important port as the gateway to the Mississippi River, but there was little other economic development because the city lacked a prosperous hinterland. In 1763, Louisiana was ceded to Spain around New Orleans and west of the Mississippi River. In the 1780s, the western border of the newly independent United States stretched to the Mississippi River. The United States reached an agreement with Spain for
History of St. Louis (1763–1803) Louisiana Purchase. The treaty was ratified by the U.S. Senate in November 1803, and the transfer of power from Spain was made official in St. Louis at a ceremony called Three Flags Day. On March 8, 1804, the flag of Spain was lowered at the government buildings in St. Louis and, according to local tradition, the flag of France was raised. On March 10, 1804, the French flag was replaced by the flag of the United States. History of St. Louis (1763–1803) The history of St. Louis, Missouri from 1763 to 1803 was marked by the transfer of French Louisiana