The basic thesis is obvious, and the author fails to build a coherent narrative based on geography. He has some very non-geographical political opinions that come off as fearful hysteria rather than adding to the topic of the book.
I do like the observation about the inevitability of the development of civilization when there's wide, flat land with easily navigable rivers vs. the obstacles Africa has had historically due to its many waterfalls along its waterways. However, no coherent formula or mechanism was described for how technology and culture often overcome geographic factors. This book presents a thesis, doesn't support it well, and is only descriptive, rather than providing a prescriptive model for understanding new situations.
He adds a bit about space at the end that's pointless. An interesting discussion could have been about the geographies involved between points of interest: Earth, Mars, the asteroid belt, moons, la Grange points, etc.