The united states bought the louisiana territory in 1803. it doubled the size of the united states. this was land that no one had yet explored. president jefferson sent meriwether lewis and william clark to explore it. these two men brought back information about the plants, animals, and other resources of the west. the word spread quickly that lewis and clark had found land that was rich in furs. they had also found a way to get there by water, using the missouri river. lewis and clark were the first to explore much of this river. by the spring of 1806, many adventurers and trappers were going to st. louis. from this city, they could travel on the missouri river to the new lands in the west. how was lewis and clark's exploration of the missouri river important for westward expansion?