John McNeill's Mosquito Empires, the deserved winner of the 2011 Albert J. Beveridge prize of the American Historical Association, is a very important contribution to the burgeoning literature in the field of environmental history. It certainly merits a review in a journal devoted to comparative studies because it crosses both disciplinary and geographical boundaries. It unites research in military history, political history, parasitology, virology, meteorology, and ecology in support of a simple but compelling hypothesis, namely that differential immunity to yellow fever and malaria, both diseases spread by mosquitoes, gave people who were already resident in the New World an advantage over new arrivals. McNeill demonstrates convincingly that this advantage benefited the established Spanish colonial regime in the New World against invaders from north European countries like Britain and France until about 1770. Thereafter, it helped revolutionary movements all over the Americas in their struggles for independence from the Old World. McNeill shows that the ecology of diseases transmitted by mosquitoes made a difference to the battle of Yorktown in 1781 (the culmination of the American War of Independence), the struggles of Toussaint Louverture in Haiti, and the campaigns of Simon Bolívar in South America. By bringing all these conflicts together, Mosquito Empires succeeds in uniting the history of regions such as the United States and the northern parts of South America, which are frequently studied separately, into a single historical-ecological framework provided by the concept of the Greater Caribbean.

To this reviewer, a specialist in European history, McNeill's book invites still wider geographic comparisons, in particular with broadly similar phenomena in earlier periods of European history that are unfortunately less documented than the period covered by Mosquito Empires. In the medieval period, French and German armies, coming from countries in northern Europe where there was not so much malaria, repeatedly invaded Italy and besieged the city of Rome to try to gain control of the Papacy. Rome was surrounded by lands infested with mosquitoes and intense falciparum malaria, which time and again forced the invaders to withdraw. The medieval Papal State was too small to be described as a mosquito empire, but it certainly qualifies as a mosquito state—a state protected by mosquitoes. It is clear that people of the time recognized the part played by malaria in these events, since Godfrey of Viterbo in 1167 explicitly praised the role of Roman fever in defeating foreign invaders.Footnote ¹ Similarly, McNeill shows that participants in the events he describes were often well aware of the role of disease, even if modern historians have frequently ignored explicit statements to that effect in the New World sources, just as some historians choose to ignore malaria's role in Italian history.