Undaunted Courage, published in 1996, was the first in-depth book about the Lewis and Clark expedition. By the early 1990s, when Ambrose first began to consider the project, no new works had appeared in about twenty-five years, even though a great deal of new research had emerged, including a revised edition of the letters and journals of the expedition members. As the reviewer for Publishers Weekly pointed out, the "journals of the expedition, most written by Clark, are one of the treasures of American history." Ambrose decided to use this material to write an updated account of the Lewis and Clark expedition.

Undaunted Courage, as numerous critics agreed, earned its lofty title. An immediate critical and commercial success, Ambrose's vivid retelling of this historic event captivated readers and reviewers alike. According to Dale L. Walker writing in Wild West, Ambrose provided a "meticulous reconstruction" of the journey...