When President Thomas Jefferson asked Meriwether Lewis to lead an expedition west, Lewis wrote a letter to his friend William Clark. Lewis asked Clark to help command the expedition. Clark accepted eagerly. Find out more in The Lewis and Clark Expedition, a title in the Building Our Nation series.Building Our Nation is a series of AV2 media enhanced books. A unique book code printed on page 2 unlocks multimedia content. These books come alive with video, audio, weblinks, slideshows, activities, hands-on experiments, and much more.