Jefferson anticipated further westward settlements due to the Louisiana Purchase and arranged for the exploration and mapping of the uncharted territory. He sought to establish a U.S. claim ahead of competing European interests and to find the rumored Northwest Passage. Jefferson and others were influenced by exploration accounts of Le Page du Pratz in Louisiana (1763) and Captain James Cook in the Pacific (1784), and they persuaded Congress in 1804 to fund an expedition to explore and map the newly acquired territory to the Pacific Ocean.