Oregon Trail: A New American Journey, by Rinker Buck

Spanning two thousand miles and traversing six states from Missouri to the Pacific coast, the Oregon Trail is the route that made America. In the fifteen years before the Civil War, when 400,000 pioneers used the trail to emigrate West – scholars still regard this as the largest land migration in history – it united the coasts, doubled the size of the country, and laid the groundwork for the railroads. Today, amazingly, the trail is all but forgotten.