<P> The eastern boundary of the Louisiana purchase was the Mississippi River, from its source to the 31st parallel, though the source of the Mississippi was, at the time, unknown . The eastern boundary below the 31st parallel was unclear . The U.S. claimed the land as far as the Perdido River, and Spain claimed that the border of its Florida Colony remained the Mississippi River . In early 1804, Congress passed the Mobile Act, which recognized West Florida as part of the United States . The Adams--Onís Treaty with Spain (1819) resolved the issue upon ratification in 1821 . Today, the 31st parallel is the northern boundary of the western half of the Florida Panhandle, and the Perdido is the western boundary of Florida . </P> <P> Because the western boundary was contested at the time of the Purchase, President Jefferson immediately began to organize three missions to explore and map the new territory . All three started from the Mississippi River . The Lewis and Clark Expedition (1804) traveled up the Missouri River; the Red River Expedition (1806) explored the Red River basin; the Pike Expedition (1806) also started up the Missouri, but turned south to explore the Arkansas River watershed . The maps and journals of the explorers helped to define the boundaries during the negotiations leading to the Adams--Onís Treaty, which set the western boundary as follows: north up the Sabine River from the Gulf of Mexico to its intersection with the 32nd parallel, due north to the Red River, up the Red River to the 100th meridian, north to the Arkansas River, up the Arkansas River to its headwaters, due north to the 42nd parallel and due west to its previous boundary . </P> <P> Governing the Louisiana Territory was more difficult than acquiring it . Its European peoples, of ethnic French, Spanish and Mexican descent, were largely Catholic; in addition, there was a large population of enslaved Africans made up of a high proportion of recent arrivals, as Spain had continued the international slave trade . This was particularly true in the area of the present - day state of Louisiana, which also contained a large number of free people of color . Both present - day Arkansas and Missouri already had some slaveholders in the early 19th century . </P> <P> During this period, south Louisiana received an influx of French - speaking refugee planters, who were permitted to bring their slaves with them, and other refugees fleeing the large slave revolt in Saint - Domingue, today's Haiti . Many Southern slaveholders feared that acquisition of the new territory might inspire American - held slaves to follow the example of those in Saint - Domingue and revolt . They wanted the US government to establish laws allowing slavery in the newly acquired territory so they could be supported in taking their slaves there to undertake new agricultural enterprises, as well as to reduce the threat of future slave rebellions . </P>

Who was president when the us bought florida from spain