The Shaping of America: A Geographical Perspective on 500 Years of History: Volume II: Continental America (1800-1867) by D. W. Meinig

This volume covers the expansion of the United States from a country on the Atlantic seaboard to one that covers the continent. It was clearly organized--first showing how the country acquired the territory, then looking at patterns of settlement, and then covering the Civil War before closing by showing the US in relation to its neighbors. If you're looking for a solid geography that tracks both details and the big picture and which is well-illustrated, you won't be disappointed here. You can get a lot of history from this book, too, although it is not a full replacement for a history.