In February 1836, the bloody battle of the Alamo sent strong signals that the United States had entered a period of increased westward expansion. Four months later, Congress ordered the second group of Rotunda murals. The amendment commissioning William Powell to paint Discovery of the Mississippi by Hernando De Soto, 1541 A. D. was tacked onto a congressional appropriations bill that reveals the political milieu in which Powell was considered. In debate on the bill, congress was primarily concerned with allocating $3 million to President James Polk so that he might conclude treaty negotiations with Mexico. Pennsylvania Representative David Wilmot attempted to add his famous proviso to the bill, which would have prevented the establishment of slavery in any lands acquired by the U.S. as a result of the war. Southern statesmen, many of whom had supported the war for the explicit purpose of extending slavery into the West, managed to eventually defeat the proviso in the Senate, although it did pass in the House.
Serious contention between the North and South over the expansion of slavery was avoided when the Compromise of 1850 decided the status of lands seized by the United States during the Mexican War, allowing California to enter the union as a free state, ending the slave trade, but not slavery, in the District of Columbia, and strengthening the Fugitive Slave Law.
The Congressional debate that surrounded the March 2, 1847 commission of De Soto indicates that the painting can be viewed as a reflection of the competing interests who supported westward expansion. While other possible subjects for the painting were proposed--Rogers Clark's 1794 North Bend council and Marquette's 1691 exploration of the Mississippi, for example--Hernando De Soto's 1541 arrival at the Mississippi was selected.
In 1539, Hernando De Soto had explored much of the land that was now the subject of Congressional contention, when he and his army trekked some 4,000 miles across that part of the continent from what is now Tampa, Florida, to Texas.
In selecting Powell's proposal to use De Soto for the commissioned painting, Congress appropriated the historical claim of Charles V to the lands acquired in the war with Mexico. Powell's painting would portray De Soto as a representative of the Spanish empire, but also, and more importantly, as a prefigurement of the American empire and its aggressive mid-century acquisition, in the Mexican-American war, of the land initially claimed by De Soto for Spain. Furthermore, De Soto's generation was part of a European thrust into the New World that was in many ways a last ditch effort to prolong the medieval, Catholic, knightly tradition to which he belonged, a cavalier tradition that had begun late in the 15th century during Spain's wars to expel the Moors from the Iberian peninsula. The expulsion of unpopular racial groups had been practiced in the U. S., as well, ever since the Trail of Tears in 1838, when the Cherokee Indians of Georgia were forcibly moved west by the federal government. The conquistador/cavalier tradition--and its link to forced emigration--had flourished in the slave-holding plantation culture of the Southern states. These states in particular supported the Mexican War as a means to expand slavery into the western territories and increase their political and economic base, which were being increasingly eclipsed by northern industrialism.
William Powell himself invoked the conquistador mystique of De Soto, citing Theodore Irving's 1835 Conquest of Florida in support of his painting's historical accuracy and importance to the American cultural situation: "Of all the enterprises undertaken in [the] spirit of adventure, none has surpassed, for hardihood and variety of incident, that of the renowned Hernando de Soto, and his band of cavaliers. It was poetry put into action; it was knight-errantry of the old world carried into the depths of the American wilderness."1And indeed, the "American wilderness" was growing. By the end of the Mexican War (1846- 48), the United States had acquired 500,000 square miles of territory and had expanded from thirteen states to twenty-nine, an increase in area from about 900,000 to nearly 3, 000, 000 square miles.2 Powell's evocation of a past which reinforced contemporary U. S. expansionism and patriotism was certainly an important reason for his winning the commission from Congress. From 1847 to 1855 Powell worked on the painting, as the imperialist jingoism of Manifest Destiny reached its height. Upon its completion, De Soto took its place as the last of the eight Rotunda paintings.