human numbers increased, both positive and negative impacts of growth became
apparent. Larger populations contributed to greater military power through
larger armies. More people stimulated economic growth due to increased
numbers of producers and consumers. They pushed technological development
because some people could be freed from producing food to become craftsmen
Larger populations also provided sufficient labor to construct public works projects, such as fortifications, roads, and irrigation systems, as well as administrative centers and monuments. But larger populations also caused environmental destruction, forced migration, and conflict.
Civilizations typically arose and flourished due to the availability of resources such as fertile soils and good water, minerals for metalwork, or forests for fuel and shipbuilding. In the prosperous times that followed the exploitation of those resources, population tended to increase. That larger population then exploited the resource base to a greater degree.
At some point a threshold was reached, beyond which the resource base could no longer support the population. The resulting disruption then caused problems similar to those we see today from severe population pressures - social and economic turmoil, hunger, migration, and war.
As civilizations faced extreme resource scarcity, typically one of three things happened: they overran another civilization to secure new resources (and were often assimilated); or, in their weakened condition, they were overrun by another culture: or, they simply collapsed and their people dispersed. We can see this in our cultural birthplace in the Fertile Crescent, and the progression of civilizations that flourished and collapsed there - from Babylon, to the Hittites, to Assyria and to Persia. All of these societies committed what author Jared Diamond calls "ecological suicide."
The transition from nomadic lifestyles to agriculture and civilization as we know it began in three primary regions of the world - Southwest Asia, China, and Mesoamerica. But none of those areas could sustain the intensive agriculture necessary to support large populations, and all became increasingly degraded. Because of food scarcity, large numbers of people lived on the edge of starvation.
Resource scarcity also caused other impacts. As historian Gwynne Dyer wrote, "The basis of civilization is agriculture, which transforms the land into a valuable possession that requires protection." It is understandable then, that the first recorded war in human history was fought between two cities in the Tigris-Euphrates Valley over the movement of a boundary stone marking fields. To threaten a society’s farmland was to threaten its food supply, which was to threaten its very existence.
Since that time, countless wars have been fought over hunting grounds, farmland, forests, water, salt, minerals, or control of strategic areas or trade routes. Underlying all of these conflicts were the greater needs of greater numbers of people.
Viewed through a demographic lens, the rise and fall of civilizations fits a similar pattern. The Hyksos conquest of Egypt around 1600 B.C.E., for example, is credited to their use of horses and chariots. But driving that conquest were population growth and resource scarcity, compounded by deforestation, desertification, and soil erosion in the Hyksos’ original homelands in Syria and Palestine. When their traditional home could no longer support their population, the Hyksos seized the richest territory they knew of, which was Lower Egypt.
The expansion of the Greek Empire can be similarly linked to population pressures. By 650 B.C.E., population had increased significantly in response to the prosperity brought by trading. Unfortunately, environmental destruction - primarily manifested as deforestation and soil erosion - also increased. Plato, in his Crititas, observed that, "What now remains compared with what then existed is like the skeleton of a sick man, all the fat and soft earth having wasted away, and only the bare framework of the land being left. . ."
The combination of population growth and environmental destruction meant that the supply of farmland - and therefore food - was insufficient to meet the needs of Greece. This stimulated Greek colonization of the forest and farmlands around the Mediterranean and the Black Sea.
The rise of Rome was also profoundly affected by increasing human numbers. The fledgling civilization fought its first major wars against the Samnites of northern Italy, who were forced by population growth down into the Roman province of Campania in search of farmland. After three major wars, the Romans prevailed.
They then employed their expanded and improved army to seize additional cropland, forest areas, and mineral resources all around the Mediterranean. With a larger population, a larger army, and a booming economy due to captured resources, Rome became the world’s first great empire.
But population growth and the resulting environmental destruction also contributed to the fall of Rome. The constant need to feed more people, maintain standing armies and support a growing economy forced the Romans to overexploit their resource base.
Rome had guaranteed every citizen a daily ration of bread since 58 B.C.E. to assure political stability. To create fields to produce enough grain (and to provide construction and shipbuilding materials), forests were cleared around much of the Mediterranean. Deforestation and erosion worsened as fields were carved out on ever steeper slopes in an attempt to produce still more grain. Rome was forced to virtually abandon several major cities such as Leptis Magna, in what is now Libya, as erosion and climate change caused by deforestation destroyed their harbors and grain fields.
The Empire began gradually to contract as environmental destruction, outside military pressures, and internal dissent mounted. By the time the Roman capitol was overrun in the early fifth century C.E. by the Goths, the western Empire was only a shadow of its former glory.