Disease, Demography, and the Smallpox Catastrophe

The demographic collapse of the Andean population between 1520 and 1620 is the single most important fact about the Spanish conquest of the Inca Empire and its aftermath. The population of the Inca Empire in 1520 has been estimated at ten to twelve million; by 1620, after a century of European rule, the indigenous population of the central Andes had fallen to perhaps 600,000. The proximate cause was the introduction, by the Spanish, of a series of Eurasian epidemic diseases against which the Andean population had no acquired immunity. The most important of these were smallpox, measles, influenza, typhus, and diphtheria. A second important cause was the social disruption caused by war, displacement, and the destruction of the Inca system of redistribution. The role of European disease in the Andes is now understood to have been central to the conquest, both as a direct cause of mortality and as a destabilizing factor in Inca politics. The first smallpox epidemic of 1524–1527, in particular, killed the Sapa Inca Huayna Capac and his designated heir Ninan Cuyochi, set off the civil war of succession between Huáscar and Atahualpa, and created the political disequilibrium that the Spanish were able to exploit at Cajamarca in 1532.

Background

The Andean population in 1520

The population of the Inca Empire in 1520 has been the subject of considerable historical and archaeological investigation. The conventional estimates, derived from the work of the demographers Noble David Cook, Woodrow Borah, and their successors, are based on the counts of tributaries made by the Spanish in the 1570s and on the tribute registers of the early colonial period, projected backward to the pre-conquest period. The estimates for the central Andes range from ten to twelve million in 1520, with a further one to two million in the northern Andes (modern Ecuador and southern Colombia) and another one to two million in the southern Andes (modern Bolivia, Chile, and northwestern Argentina). The total population of the Inca Empire was on the order of twelve to fifteen million.

The population was supported by an agricultural system of considerable intensity. The Inca had developed a complex system of terracing, irrigation, and raised-field agriculture, and the highland basins of Peru and Bolivia supported population densities that were among the highest in the pre-Columbian Americas. The population of the central highlands of Peru has been estimated at perhaps 100 to 150 persons per square kilometer in 1520, comparable to the population densities of contemporary Europe. The population was, in other words, dense, sedentary, and well-nourished, and it was therefore exceptionally vulnerable to epidemic disease.

The European disease pool

The diseases that were introduced into the Andes by the Spanish were part of a larger pool of Eurasian epidemic diseases that had evolved in close contact with human populations over several millennia. Smallpox, measles, influenza, typhus, diphtheria, and whooping cough were the most important, and they had become endemic in the populations of Europe, Africa, and Asia, where mortality was high in childhood but where most adults had acquired some immunity. The populations of the Americas had been isolated from this disease pool since the initial peopling of the Americas, and they had no acquired immunity to any of the Eurasian epidemic diseases. The introduction of any of these diseases into an indigenous American population was, therefore, a catastrophic event, in which a substantial proportion of the population died. The first European disease to reach the Andes was smallpox, introduced into the Caribbean in 1518 or 1519 and spread to the mainland by 1520 or 1521. The first major epidemic in the Inca Empire occurred in 1524, when the disease was carried into the highlands by Spanish-led expeditions and by indigenous traders moving along the Qhapaq Ñan.

The first smallpox epidemic, 1524–1527

The arrival of smallpox in the Andes

The first smallpox epidemic in the Andes is conventionally dated to 1524, when the disease was carried into the interior of the empire by the Spanish-led expedition of Rodrigo de Bastidas, and possibly also by an indigenous person who had been taken to Spain and had returned. The disease, which the Inca called pupu or huyra and for which they had no word, spread along the Qhapaq Ñan from the north, and within a year or two it had reached the imperial court in the northern highlands of present-day Ecuador. The Spanish priest and chronicler Miguel Cabello Balboa, drawing on indigenous testimony, claimed that the disease killed the Sapa Inca Huayna Capac in 1527, and the date is generally accepted by modern historians.

The mortality from the first smallpox epidemic is unknown but is generally believed to have been substantial. The Spanish chroniclers report that the disease killed a great many members of the imperial household and a large proportion of the population in the highlands. Modern estimates, based on the demographic data, suggest that the first epidemic may have killed 25 to 35 percent of the population in the affected regions. The mortality was particularly high in the dense populations of the central and northern highlands, where the disease spread rapidly along the Qhapaq Ñan.

The death of Huayna Capac and the succession crisis

The death of the Sapa Inca Huayna Capac from smallpox in 1527 was the central political event of the Inca Empire in the years before the Spanish arrival. Huayna Capac had been campaigning in the north for several years, and his principal residence had been in the city of Tomebamba (modern Cuenca, Ecuador). The Spanish chronicles report that the disease, which Huayna Capac had never seen before, killed him and many of his attendants in a matter of days. The designated heir, Ninan Cuyochi, died of the same disease shortly after, and the death of the Sapa Inca without an agreed heir set off the civil war of succession between Huáscar and Atahualpa.

The civil war was, in effect, a consequence of the first smallpox epidemic. Without the epidemic, the succession would have been settled by the established procedures of the Inca state, and the empire would have remained politically stable. The Spanish, who had been informed of the epidemic and of the death of Huayna Capac by indigenous intermediaries, used the information to make alliances with the peoples of the northern Andes who had been incorporated into the empire only recently and who saw the Spanish as a means of throwing off Inca rule.

The subsequent epidemics

Smallpox, measles, and the other epidemics

The first smallpox epidemic of 1524–1527 was followed by a series of further epidemics that ravaged the Andean population over the next century. A second major epidemic of smallpox reached Peru in 1529 or 1530, just before the Spanish arrival at Cajamarca, and a third epidemic, of measles, arrived in 1531 or 1532, in time to affect the populations around the Spanish army. A series of further epidemics — of influenza in 1558, of measles in 1589, of smallpox in 1585 and again in 1595, of typhus in 1585, and of diphtheria in 1614 — followed over the next century.

Each of these epidemics was a catastrophe on its own, and the cumulative effect was the demographic collapse of the Andean population. The population of the Inca Empire, which had been on the order of ten to twelve million in 1520, had fallen to perhaps 6 million in 1550, to perhaps 3 million in 1580, and to perhaps 1.3 million in 1600. By 1620 the population of the central Andes had fallen to about 600,000, a loss of about 95 percent from the pre-conquest level.

The role of European disease

The role of European disease in the Andes is now understood to have been central to the conquest and its aftermath. The introduction of Eurasian epidemic diseases into a population with no acquired immunity was, in itself, a catastrophe, and the demographic collapse of the Andean population is now understood as a direct consequence of this introduction. The Spanish, who were the agents of the introduction, were not the cause of the collapse in the sense of intentional action, but they were the cause in the sense that they were the agents by which the diseases were brought into the Andes.

The role of European disease in the conquest was not limited to the direct mortality. The first smallpox epidemic of 1524–1527 had destabilized the Inca state, and the subsequent epidemics continued to destabilize the indigenous societies of the Andes throughout the colonial period. The Spanish used the epidemics, intentionally or unintentionally, as a tool of conquest: the news of the epidemic that had killed Huayna Capac was used by the Spanish to frighten the Andean population, and the subsequent epidemics of measles, influenza, and other diseases weakened the indigenous resistance to Spanish rule.

The demographic collapse

The scale of the collapse

The demographic collapse of the Andean population is one of the most thoroughly documented cases of epidemic catastrophe in the pre-modern world. The figures, derived from the work of the demographers Cook, Borah, and their successors, are based on the counts of tributaries made by the Spanish in the 1570s and on the tribute registers of the early colonial period, projected backward to the pre-conquest period. The historian Noble David Cook has estimated that the total indigenous population of central Peru fell from about 9.5 million in 1520 to about 1.3 million in 1620, a loss of about 86 percent. The figures for Bolivia and Ecuador are of similar magnitude. The demographic collapse was on the order of 85 to 95 percent over a century.

The collapse was not uniform. The first major wave of mortality occurred in 1524–1527, with the first smallpox epidemic, and the second major wave occurred in 1529–1532, with the second smallpox epidemic and the measles epidemic. A third major wave occurred in the 1550s and 1560s, with epidemics of influenza and other diseases, and a fourth major wave occurred in the 1580s and 1590s, with epidemics of measles, smallpox, and typhus. A final major wave occurred in the early seventeenth century, with epidemics of diphtheria and other diseases, and the demographic collapse was largely complete by 1620.

The causes of the collapse

The demographic collapse of the Andean population had several causes. The most important was the introduction of Eurasian epidemic diseases against which the Andean population had no acquired immunity. A second important cause was the social disruption caused by war, displacement, and the destruction of the Inca system of redistribution. The Inca had maintained a complex system of state granaries and storehouses, in which food was stored in years of good harvest and redistributed in years of poor harvest, and the system was an important buffer against famine. The Spanish conquest destroyed the system, and the destruction of the buffer contributed to the mortality of the epidemics.

A third important cause was the Spanish policy of forced labor. The colonial mita, a rotating labor draft that sent some 13,000 workers a year to the silver mines of Potosí, was a major cause of mortality in the highland population. The mortality rate among the mitayos has been estimated at between a quarter and a half over the period of service, and the cumulative effect of the mita on the highland population was substantial.

The consequences of the collapse

Political consequences

The demographic collapse of the Andean population had important political consequences. The Inca had relied on a complex structure of labor extraction, in which the mit’a obligation was distributed across a large population. The disappearance of perhaps nine-tenths of the population by the early seventeenth century meant that the colonial authorities, although they inherited the mit’a system and adapted it to their own purposes as the colonial mita, had to do so with a much smaller labor pool. The collapse of the labor pool had consequences for the Spanish colonial economy, which was forced to reorganize itself around a much smaller population.

The demographic collapse also had consequences for the indigenous political system. The Inca had maintained a system of provincial administration, in which groups of households were overseen by officials appointed from Cusco. The demographic collapse meant that the units could no longer be maintained. The Spanish, who inherited the system, were forced to reorganize the provinces and to consolidate the smaller units, and the reorganization contributed to the social disruption of the colonial period.

Cultural and religious consequences

The demographic collapse also had cultural and religious consequences. The Inca had maintained a complex system of state religion, centered on the cult of the Inti, the sun, and the cult of the royal mummies of the deceased Sapa Incas. The system required a substantial body of full-time religious specialists, and the collapse of the population meant that the system could no longer be maintained. The Spanish suppression of the Inti cult in the 1570s effectively dismantled the indigenous state religion in the highlands within two generations of the conquest. The collapse also had consequences for the indigenous languages: the disappearance of many of the smaller languages of the central Andes has been attributed to the demographic collapse, and the spread of Quechua and Aymara over a much larger area was, in part, a consequence of that disappearance. The survival of Quechua and Aymara as major languages of the Andes is, in this sense, a consequence of the demographic collapse.

Significance

A central feature of the conquest

The demographic collapse of the Andean population is now understood to have been a central feature of the Spanish conquest of the Inca Empire. The first smallpox epidemic of 1524–1527 was one of the principal causes of the political disequilibrium that the Spanish were able to exploit in 1532, and the subsequent epidemics of measles, influenza, and other diseases weakened the indigenous resistance to Spanish rule throughout the colonial period. The demographic collapse, in other words, was not a consequence of the conquest but a cause of it.

The collapse also has continuing consequences. The modern Andean population is descended from a small fraction of the pre-conquest population, and the genetic and linguistic legacy of the collapse is visible in the modern distribution of indigenous languages and communities. The legacy of the conquest is, in this sense, a continuing condition of Andean life, and the demographic collapse is one of its most fundamental features.

A model for understanding other cases

The Andean case has been important for the study of epidemic disease and demographic collapse elsewhere in the Americas. The introduction of Eurasian epidemic diseases into populations with no acquired immunity was a general phenomenon, and the cases of Mexico, Central America, and the Caribbean have been studied in parallel with the Andean case. The Andean case, in particular, has been important for the study of the political and economic consequences of demographic collapse. The study of the Andean demographic collapse is, in this sense, a study of the legacy of the Spanish conquest in its most fundamental form.