Ecological Imperialism , written by Alfred W. Crosby, is a study in the science of ecological history, which attempts to find out what caused the environmental consequences of history. Crosby's main point in this book is that it was more the Old World diseases, animals, and plants that kept non-European people from resisting against Western colonialism than it was the European military power. Therefore, the defeat of the American Indian nations was as much a biological conquest for Europe as it was a military and cultural conquest.
Although European weapons, cavalry charges, soldiers dressed in armor, and the raging beasts (horses), played a huge role in the history of Stone Age warriors, the introduction of animals and new grains was just as important to the Neolithic Revolution. It also played a bigger importance in the defeat of the New World. Another significant occurrence that has to be mentioned in the imperialist conquest is the devastating effects of foreign diseases on the bodies and religions of the people who tried to resist invasion. Millions of native Australians, New Zealanders, and Americans died of smallpox, measles, and other diseases during the entire period of European colonization. The results of the trouble of supply sources and moral played right into the hands of the conquerors. Crosby also points out how the English felt that the reason the natives were dying off so quickly, was because it was the English god that made them die so fast. This was a perfect example of how Europeans demoralized the beliefs of non-European and non-Christian people.
Crosby marks out the history of Western expansion from the Crusades through the colonization of the Canary Islands, the Western Hemisphere, Oceania and Africa. In many instances, the native plants, animals, and people were altered to such an extent that the outcome of the ecosystems looked like that of Europe more than the native country.