For the history of the American West, Richard Slotkin's trilogy on the history of the West is absolutely a must. They are Regeneration Through Violence: the Mythology of the American Frontier, 1600-1860, The Fatal Environment: the myth of the frontier in the age of industrialization, 1800-1890, and Gunfighter nation: The myth of the frontier in twentieth-century America. The last one especially is absolutely fascinating, as it isn't simply a history of the West, but rather a cultural history of what the idea of the West and the frontier has meant in the American psyche as reflected in media representations since then such as books and movies. Definitely look into those, they will offer you some great perspective!