In this classic work, Goetzmann argues that the exploration of the American West was not a series of haphazard adventures motivated by personal gain, but rather a series of carefully planned missions to promote the national good. He draws on the diaries and letters of explorers to contrast the early American expeditions, sponsored by the federal government to promote national development, with private British ventures, such as the Hudson's Bay Company, which sought commercial gain. Meriwether Lewis and William Clark were the first explorers with a broad and explicit sense of national purpose, setting out in 1804 with instructions from President Thomas Jefferson to collect information "covering the whole range of natural history from geology to Indian vocabularies." And as Lewis and Clark traveled toward the American Northwest, William Dunbar and Dr. George Hunter journeyed south to collect information on the newly acquired Louisiana Territory. Two major eras of Western exploration followed the one launched by Lewis and Clark: the period of settlement and investment (1845-1860) and the era of the great surveys (1860-1900). During the first of these, explorers such as John B. Weller and John Russell Bartlett became political diplomats as well as discoverers as they surveyed the boundary between the U.S. and Mexico. During the second period, explorers were no longer discoverers or diplomats, but academic scientists, such as Josiah Dwight Whitney, whose philosophy influenced twentieth-century attitudes toward conservation and the environment.