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 to an egalitarian French government. In a show of strength, the Spanish governor sent a fleet of galleys and soldiers with military supplies to reinforce Spanish control of St. Louis. However, even while the Spanish colonial officials were trying to maintain control of Louisiana, the Spanish government was attempting to transfer the territory to France. The Spanish government secretly returned the unprofitable Louisiana territory to France in October 1800 in the Treaty of San Ildefonso. After a promise by French leader Napoleon Bonaparte not to sell Louisiana without giving Spain the right of first refusal, the Spanish officially transferred