This book is really well done, a masterful dissection of a complicated issue.
General themes abound.
The role of the government is critical, for two major reasons. Land grants and sales were fundamental revenue sources or incentives to settlement and development. This goal was so expensive that the only organization able to fund it was the federal government. Westerners would have more people in their territories, which would give them more tax revenue and more power in Congress. Unfortunately, as in many historical immigration situations, the people who arrived first, or the people with the most capital, receives a vast competitive edge.