“It is to the ecologist and not to the philatelist that the historian should look for his model of scholarly virtue.”

Crosby suggests that historians’ work should be more interdisciplinary and inclusive of scientific research. He elevates the work of ecologists over that of stamp collectors to make his point; rather than just reflecting names and figures that were deemed worthy of commemoration on stamps by government leaders, history should study the impact of events and actors upon the land. His work is one of the first studies to integrate history and ecology by examining historical humans through a biological lens to understand how humans both impact their environments and are shaped by them.

“Thus it was decided by Rome that the aborigines of America were worthy of conquest and too worthy to be treated as domesticated animals. Again and again during the centuries of European imperialism, the Christian view that all men are brothers was to lead to persecution of non-Europeans […]”

The Church justified the subordination of Indigenous groups by concluding that God created them, along with the rest of humankind, in a monolithic creation. Although Europeans were puzzled by the distinctions between the continents, they ultimately had to incorporate Indigenous people into the Christian worldview if colonization were to succeed. Spain’s Catholic monarchs viewed the conquest of the Americas as a continuation of the Reconquista in Spain, the nearly eight-century battle to claim the Iberian Peninsula for Catholicism. Thus, the Indigenous people of the region were forced to convert to Catholicism, and the conquest was both territorial and religious.