The Lewis and Clark Expedition is one of the foundational stories of American westward expansion, but the standard telling consistently underestimates the contributions of two people without whom the entire enterprise would almost certainly have failed. Sacagawea, the young Shoshone woman who joined the expedition with her infant son, and York, the enslaved Black man who was William Clark's lifelong companion, played roles far more critical than the subordinate positions history has traditionally assigned them. Sacagawea's contributions went far beyond the popular image of a passive guide pointing the way west. Her presence fundamentally changed how Indigenous nations perceived the expedition. A military party traveling with a young woman and a baby was clearly not a war party, and this visual signal of peaceful intent opened doors that armed men a ...