In his article, Infectious Disease and the Demography of the Atlantic Peoples, Alfred W. Crosby argues that population densities in the Americas in pre-Columbian times were probably equal to those in Asia, and even greater when compared to Africa. Although he admits that the inhabitants of the Americas occupied the land for only eleven thousand years (and that is not long, compared to the Old World), he is certain that there were not many large areas with good climate and soil fertility that were not occupied before Christopher Columbus arrived. Thereby he creates a paradox: If the New World was as heavily populated as he writes, how could the migration from the Old World be so enormous? Although ships, and later, planes provided the possibility to transport hundreds of people very fast, Crosby thinks that it was not the machines that played the lead role in the transatlantic transfer.
Crosby presumes that Columbus’s plans for the New World were not colonization and slaughter, but trade and profit for both sides. Nevertheless, with the attack of epidemics, the plans needed to be changed. Europeans needed slaves to maintain plantations, but the native peoples died rapidly. The epidemics that Europeans brought with them were the reason why the native population of the Americas died, argues Crosby. The lowland population numbers fell from the diseases that the highland population had to endure, but also from the maladies that existed in the tropics of the Old World. The native peoples of the Americas fell ill and died so quickly that the Europeans had to find another way to conquer the New World. There were 80 million people living in Europe when Columbus began his journey; there were around 180 million people by 1800. The population of the British Isles sailed to Australia, New Zealand, and the Americas. Aboriginal populations, points out Crosby, had no resistance to the epidemics the Europeans brought; Europeans, however, were more or less resistant to them, and health practices decreased the spread of disease. The biggest transfer of Europeans happened later when an American fungus spread through the potato fields of Europe.
More than a million Irish died; others fled to the United States, and so did Germans, Scandinavians, and, later, Southern Europeans and Slavs. It is very easy to believe that the people sought salvation in the New World, especially when a new disease had exterminated millions of Europeans; however, Crosby does not explain why Southern Europeans, Ashkenazim, and Slavs, although they did not face the disease, followed the Irish. It could be explained as mass panic, but in the mid-1840s, the news was not forwarded so rapidly as happens now; such immigration was probably more difficult for Southern Europeans than for Germans or Scandinavians, due to their geographic location. As there were no jets back in the 1840s, one had to have a very pressing reason to go on such a long-distance journey to escape a disease one had not yet encountered. Crosby’s arguments are persuasive, but additional sources or quotations could be provided to increase the reliability of his assumptions. It should be stressed that the given example is probably the one I find a little doubtful; others, however, are quite convincing, since the native population of the Americas indeed had no way to escape the epidemics Europeans brought with them, and their high mortality rates were the consequence.