In 1803 the United States doubled in size as the result of the Louisiana Purchase. A year later the dominant movement in American society of the nineteenth century, westward expansion, originated with the men that President Thomas Jefferson sent out to explore the newly won territory, the famous expedition led by Meriwether Lewis and William Clark. Together the two men actively contributed to only one book, History of the Expedition under the Command of Captains Lewis and Clark, to the Sources of the Missouri, thence Across the Rocky Mountains and down the River Columbia to the Pacific Ocean (1814), which was published five years after Lewis's death. But there are few schoolchildren in the United States who have not heard some version of their story. The significance of their success in American history is undeniable. As Archibald Hanna states in his introduction to the 1961 edition, Lewis and Clark started "the...