The themes of exploration and expansion are central to Undaunted Courage and the Lewis and Clark expedition. In 1790, the United States extended only to the eastern bank of the Mississippi River. Although the lands to the west were largely unexplored, they captivated the interest of many Americans for several reasons. At the dawn of the 19th century, a pioneering spirit was still a fundamental aspect of the American identity. Additionally, many individuals desired to settle on and cultivate their own land, but the availability of plots was constrained by the growing populations in the east. Moreover, a sense of nationalism was on the rise, with many Americans believing that the United States should expand across the continent from the Atlantic to the Pacific Ocean. The Louisiana Purchase officially made vast amounts of land accessible to American settlers, even though Native American tribes considered these western territories their own. The expeditions of Lewis and Clark, along with Zebulon Pike's exploration of the upper Mississippi Valley, sparked increased interest among Americans in settling these lands. In this regard, Lewis was truly an architect of empire building.

Undaunted Courage offers significant insights into the sense of superiority that many white Americans in the nineteenth century felt over non-white individuals. Despite these prevailing attitudes, politicians like Jefferson aimed to integrate American Indians into the broader society. However, Jefferson's motives were not entirely selfless. He anticipated that white settlers would encroach on American Indian territories, leaving him with two choices: to "civilize" the Indians or relocate them to reservations. His policy concerning American Indians was based on the idea of their eventual assimilation into white culture. Jefferson believed that Indians could be molded into responsible American citizens, abandoning their traditional ways to become farmers or traders.

As Jefferson's leading Indian agent, Lewis endorsed these plans. He delivered speeches to each tribe, introducing Jefferson as their new "Great White Father." He emphasized the need for Indians to respect the United States' power and participate in its proposed commercial activities. Lewis instructed the tribes to make peace with one another and was perplexed when they did not comply. Throughout the journey, Lewis rarely viewed the Indians as individuals. For example, he insisted on appointing a primary chief, even when no such leader existed.

Undaunted Courage also addresses the perspectives on African Americans. Early in the book, Ambrose cites Jefferson's Notes on the State of Virginia: "The whole commerce between master and slave is a perpetual exercise of...the most unremitting despotism on the one part, and degrading submissions on the other." Although Jefferson, a slaveholder, wanted to see the end of slavery, he did not wish for this to occur during his lifetime, believing his generation was unprepared for such a drastic change. Similarly, Lewis, also a slaveholder, did not consider African Americans capable of becoming American citizens.

The pervasive racism is evident throughout the book, particularly in the account of York, Clark's slave. York endured the same risks as every member of the Corps of Discovery. Yet, after the expedition, when York requested his freedom as a reward for his service, Clark denied his plea. Clark also refused York's request to move to Louisville, Kentucky, to be with his wife, and to hire himself out for Clark's benefit. As Ambrose succinctly expresses, York risked his life to save Clark's, journeyed across the continent, and returned with his childhood friend, only to be punished for being insolent and sulky, and denied not only his freedom but also his family, including his wife and, presumably, children.

The members of the Corps of Discovery ventured into territories uninhabited by...