The relationship between nomads and settled people was a driving force throughout history. At times, conflict replaced trade when new nomadic people moved into an area. Nomads might attack settlements or even organize a large enough force to topple great civilizations. Once they conquered a civilization, however, they in turn became settled peoples, giving up the nomadic way of life.

Civilizations Change

All societies and civilizations change. In fact, history itself might be defined as the story of these changes. Ancient civilization changed in many ways over time. Among the chief causes of change were shifts in the physical environment and interactions among people.

The Effect of the Environment

Like their Stone Age ancestors, people in early civilizations depended heavily on the physical environment. They needed ample rain and fertile soil to produce crops. Significant changes in the environment could have an immediate impact on people's lives.

This store room in Pompeii shows various bowls and the remains of one person who was buried alive after a volcano rained hot ash down on the ancient city.

At times, sudden, drastic events such as an earthquake, flood, or volcano could devastate a community. Survivors had to rebuild on the ruins. Farming the same land year after year could reduce soil fertility. Silt could clog rivers, making waters too salty. Environmental catastrophes—whether sudden or slow—could force people to abandon cities and migrate to new areas.

Cities needed resources such as stone, timber, and metals, along with land. If people used up all the local timber or ran out of other building resources, they would have to adapt to this scarcity. They might, for example, trade with areas where such resources were available. Or they might use alternate building materials such as reeds.

Cultural Diffusion

Change often came as a result of cultural diffusion, the spread of ideas, customs, and technologies from one people to another. Cultural diffusion occurred through migration, trade, and warfare.

As famine, drought, or other disasters led people to migrate, they interacted with other people whose cultures differed from their own. As a result of such interactions, people often shared and adapted skills, customs, and ideas. In prehistoric times, migrating people could have shared technologies that led to farming.

As people settled in cities, trade increased. Trade is one of the greatest forces for cultural diffusion because it introduces people to new goods, ideas, and technologies. In ancient times, skills such as bronze-making and writing passed from one society to another through trade. Traders spread religious beliefs, artistic styles, and oral histories.

Warfare brought change too. Often, victorious armies imposed their rule and culture on the people they defeated. Sometimes, though, the process worked in reverse. Nomadic conquerors were often absorbed into city life.

In China, for example, conquering people were often absorbed by China's more advanced civilization. To avoid this, some nomadic rulers lived in camps outside the city, keeping their own customs.

Cities Become City-States

Some Neolithic cities expanded to become city-states. A city-state is a political unit that includes a city and its surrounding lands and villages. Peasants in these surrounding lands had to give a significant portion of each harvest to support the government and temples. Sumerian civilization in the Tigris-Euphrates Valley consisted of a number of rival city-states.

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