It clearly defines how place and demographic movements impacted the greater country. It is a must read for those interested in American West history and historical geographers.
The thesis is a great, if controversial, work of American historical geography. Some revisionists point-out that the thesis ignores American Indian movement from the Alaska down and Spanish expansion into the American Southwest. However, while these cases are part of American history they do not have as great an impact on the establishment of the American system which is still heavily based on English American colonial experience with other European groups having smaller impacts locally. American Indians either live in "regular" towns and cities or they live on reservations established on the American system during Western expansion. Spanish Americans meanwhile are integrated into the American popular culture while the recent wave of Hispano immigrants have no ties to the original Spanish/Mexican establishment in the United States.
A thing to ponder is what will happen to American culture now that there is no frontier? Westerners who still idolize expansion complain "city-folk" and "suburban-folk" have lost their Independence and rely too much on vertical systems. What ever is to come, one must acknowledge how the frontier help make America what it is today.