Colonial Latin America and the circum-Caribbean Central Mexico is the most intensively studied region regarding the impact of European diseases on indigenous demography Where in 1520 there lived an estimated 25 million native peoples, in 1620 there lived some 730,000—a decline of 97 percent, attributed overwhelmingly to disease Similar catastrophes unfolded across the hemisphere The most precipitous decline is thought to have occurred in the Caribbean, where the precontact indigenous population of several millions had been all but exterminated by the 1550s Such diseases spread rapidly in all directions, preceding and accompanying military incursions, weakening indigenous polities, and facilitating the process of conquest and colonization in the Caribbean, Mexico, the Andes, Brazil, New England, and beyond This process of demographic catastrophe, an unintended consequence of the European encounter with the Western Hemisphere, affected every aspect of the subsequent history of the Americas In the English-speaking world, the predominant view for centuries regarding Indian depopulation in postconquest Spanish America centered on the “Black Legend” of Spanish atrocities, a view most forcefully articulated and propagated by the Spanish bishop Bartolomé de Las Casas in the 1500s By the early 2000s, a scholarly consensus had emerged that the principal cause of indigenous population declines was in fact pandemic and epidemic diseases The exact sequence and timing varied greatly from place to place Every locale had its unique history of demographic decline, with periodic outbreaks of various pathogens: smallpox, measles, typhus, influenza, yellow fever, diphtheria, bubonic plague, malaria, and others Far and away the deadliest killer was smallpox, the first documented New World outbreak occurring in the Caribbean in 1518 Spanish friars, reporting to King Charles V in January 1519, estimated that the disease had already killed nearly one-third of Hispaniola’s Indians and had spread to Puerto Rico In these earliest outbreaks, influenza probably accompanied the spread of smallpox By the early 1520s, three principal disease vectors, mainly of smallpox and influenza, were spreading rapidly through indigenous populations One had entered through northern South America near the junction with the Central American isthmus, and by the late 1520s had spread far into the interior along the northern Andes The second had entered along the gulf coast of Mexico, from Yucatán to present-day Veracruz, and by mid-1521 was decimating the population of the Aztec capital of Tenochtitlán By the late 1520s, epidemics in the Americas 123 this second vector had bifurcated, spreading south into Central America and north into western and northern Mexico, where it was poised to sweep farther north The third disease vector was launched with the first exploratory expeditions along the Pacific coast of Central America and Peru, beginning in the early 1520s By the late 1520s, this third vector had also bifurcated, spreading north through Nicaragua and Guatemala, and in less than a decade racing 3,000 miles south down the Andes, reaching as far as southern Bolivia A fourth set of vectors began spreading inland from the Brazilian coast from the beginning of permanent settlements in the early 1550s By the late 1550s and early 1560s, the epidemics had spread along much of the Brazilian coast and were sweeping into the interior Widespread death from disease weakened indigenous polities, engendering profound cultural crises and facilitating processes of conquest and colonization The most dramatic and extensively documented such instance occurred in Tenochtitlán during the conquest of Mexico, where a major smallpox outbreak coincided with the Spanish invaders’ siege of the island city From May to August 1521, as many as 100,000 of the city’s inhabitants succumbed to the disease The smallpox virus typically enters the victim’s respiratory tract, where it incubates for eight to 10 days, followed by fever and general malaise, then the eruptions of papules, then vesicles, and finally large weeping pustules covering the entire body, followed soon after by death Scholars agree that this smallpox epidemic, occurring just as their empire and capital city were under assault by the Spanish and their Indian allies, fatally weakened the Aztec capacity to mount an effective resistance A similar if distinctive dynamic is thought to have unfolded before and during the conquest of Peru Again, the timing of the Spanish invasion could not have been more propitious Less than a decade before the incursion of Francisco Pizarro in 1532, the vast Inca Empire was in relative tranquility under a unified ruling house Around 1525–28, at the height of the Inca Huayna-Capac’s northern campaign against recalcitrant indigenous polities around Quito, an unknown pestilence, probably smallpox, ravaged the northern zones During this epidemic, the Inca was struck by fever and died Spanish chronicler Pedro de Cieza de León recorded that the first outbreak of the disease around Quito killed more than 200,000 people Other chroniclers offered similar descriptions of a wave of pestilence in the northern districts during this same period HuaynaCapac’s death set in motion a crisis of dynastic succession and civil war that Pizarro deftly exploited to the