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
French colonization of Texas Fontainebleau, following its defeat by Great Britain in the Seven Years' War. It ceded New France to Britain. In 1803, three years after Spain had returned Louisiana to France, Napoleon sold the territory to the United States. The original agreement between Spain and France had not explicitly specified the borders of Louisiana, and the descriptions in the documents were ambiguous and contradictory. The United States insisted that its purchase included all of the territory France had claimed, including all of Texas. The dispute was not resolved until the Adams-Onís Treaty of 1819, in which Spain ceded Florida to the United