Facing The Future: People and the Planet

Setbacks

The Great Wall of China and the Sack of Rome

Population pressures have always shaped human history. The connections are not always obvious, however, because they may be quite slow-acting. Consider how construction of the Great Wall of China ultimately led to the sack of Rome.

In the third century B.C.E., a civilization of nomadic warriors flourished in Mongolia. The Chinese called these people Hsiang-Nu, but in the west, they became known as the Huns. As their population increased, the Huns gradually moved south, and began to raid China.

The Chinese responded by building the Great Wall. The Huns continued to raid around the Wall, and the Chinese ultimately had to extend their defenses. They captured and fortified the Tarim Basin all the way to foothills of the Pamir Mountains. Unable to penetrate this barrier, the Huns were forced west into Central Asia.

A few centuries later, another group of nomadic warriors arose in Mongolia. The Chinese called these people the Juan-Juan, but modern historians call them the Avars. The Avars also raided south, were unable to penetrate the Great Wall, and were forced west.

In Central Asia, the Avars collided with the Huns. The Avars, with a major technological advantage (the stirrup, which makes fighting from horseback much more efficient), defeated the Huns and drove them further west. At the Dnieper River, the Huns collided with the Goths, who were being held out of the Roman Empire by a combination of treaties, bribes, and Roman Legions. When the Huns fell on the Goths, they slaughtered them in great numbers, and drove the survivors across the river into Roman territory.

Once the Goths had penetrated the Empire, they found it an empty shell. They smashed through southern Europe, crushed the remaining Roman Legions, and sacked the capital in 410 C.E.

Population growth was not always linear. Famine, war, or disease often decimated local or regional cultures. In fact, as population grew, another pattern of human history emerged - natural and human-induced disasters that killed large numbers of people.

Historically, human numbers were greatly limited by disease. This was especially true as growing populations became more concentrated in cities, where people were more easily exposed to infectious agents. (It takes a minimum population for diseases to sustain themselves. Measles, for example, requires about 7,000 susceptible individuals to assure its survival. A regional population of from 300,000 to 400,000, with regular contact, is probably the minimum necessary to sustain that disease.)

Plague devastated Athens in 429 B.C.E., and large parts of China 200 years later. It ravaged the Roman Empire from 160 to 184 C.E., killed a large percentage of the population of Constantinople in 542 C.E., and reached Britain by 547. By the end of that cycle in 594, the population of Europe had been halved. Plague returned periodically, peaking in the fourteenth century, when it killed an estimated one third of the population of Europe.

Other diseases were equally devastating, if more localized. When Spanish conquistadors invaded Mexico in 1517, the native population was perhaps 25 million. In less than a century, it had fallen to just over one million due to introduced diseases, such as measles. In South America, the introduction of smallpox by Europeans damaged the Inca Empire so badly that Pizarro’s few soldiers, horses, and guns easily toppled it.

Famine also slowed population growth, appearing regularly around the world from the earliest times of recorded history. The Near Eastern and Mediterranean worlds were always susceptible to famine, as indicated by Biblical references.

Famine was an integral part of Roman history, and closely linked to the final collapse of the Empire. As its population grew, and environmental destruction limited local productivity, the Empire became dependent on foreign sources of grain. As the Empire contracted - and grain–producing lands in Germany, Egypt, and Britain were lost - Roman authorities were unable to provide the guaranteed distribution of food that had long maintained domestic stability. Between 400 and 800 C.E., the population of the city of Rome fell by over 90 percent, largely because of famine.Large-scale famine also occurred in the Byzantine Empire in 927, in Japan in 1232, Germany and Italy in 1258, England in 1294 and 1555, all of Western Europe in 1315, Russia in 1603, Bengal in 1669 and 1769, Ireland in 1845-49, and China and India in 1876 and 1879. Tens of millions died in these events, sometimes reducing local populations by as much as one third or more.Despite these setbacks, however, population continued to grow overall. By 1500, world population had reached an estimated 500 million. It was around this time that the era of western colonial expansion began in earnest, driven by the demands of more people for more resources.

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