This is an excellent book on how and why the Europeans were able to conquer North America, Australia, temperate South America (particularly Argentina), and New Zealand--the so-called Neo-Europes, in Crossby's terminology. Crossby's thesis is simple: the native biota of those places (including humans, of course) did not coevolve with the invaders, and were consequently naive (i.e, unequipped) to deal with them. Or, put another way, the invaders were preadapted to deal with the new conditions, and aggresively advanced, in a teamlike fashion, to encroach the native biota. Crossby also explains why Europeans were not able to conquer other places (such as Greenland, the Labrador region, and the New and Old Worlds tropics), adducing mainly climatic reasons and the lack of technological expertise.
To be sure, Crossby's arguments are not new. However, he does a great job at synthesizing an incredible wealth of historical data. His style, oftentimes humorous, also makes of his book an enjoyable read. I would recommend this book to anyone teaching a comprehensive course on the conquest of the places Crossby deals with. It is a much neglected fact that biology played a crucial role in expanding European culture.