Environmental Consequences of Connectivity


AP Theme

Humans and the Environment

Learning Objective 2.6 K

Explain the environmental effects of the various networks of exchange in Afro-Eurasia from c. 1200 to c. 1450.

Historical Development 1

Crop Diffusion Diversified Food Supplies

Historical Development 2

Disease Transferred Through Trade Routes


Global commerce led to various environmental effects across Afro-Eurasia. These changes included the diffusion of crops and animals and the diffusion of diseases. As new food crops diffused across trade routes, food supplies increased. As a result, populations expanded and became healthier. Global commerce also led to mass death. Most notably, in the mid 14th century, when the Black Death swept across Afro-Eurasia killing millions.

Crop Diffusion Diversified Food Supplies

Across Afro-Eurasia, a variety of crops made their way to new locations through trading networks. As new food sources became available, people’s diets diversified. As nutrient variety became available to more people, Afro-Eurasia societies increased their agricultural output, allowing individuals to increase their daily caloric intake. As a result,  it also became easier for communities to prevent famines. If one crop failed, other crops and nutrition sources could feed populations until the following year’s harvest. 

The following are significant crops that diffused through exchange networks before the 16th century.

Champa rice

Champa rice originated in the Champa kingdom of Southern Vietnam. Champa rice first arrived in China after the Champa kingdom sent it to the Chinese emperor as a tribute gift. Champa rice had several benefits. It was drought-resistant and could grow with much less water than traditional Chinese rice varieties. It was also fast-growing. One farmer could produce two crops of Champa rice instead of the usual once yearly harvest. After adopting Champa rice, the Chinese population began to increase, doubling within just a few centuries. 

Bananas in Africa

Bananas originated in Southeast Asia on the Indonesian archipelago. They were brought to the east coast of Africa by Indonesian seafarers across the Indian ocean. Bananas grew well in the tropical areas of Africa. The introduction of Bananas to the African continent resulted in significant demographic changes. First, because of banana’s high nutrient density, the population in Africa spiked. Bananas also increased available nutrients if the yam harvest failed. The cultivation of Bananas across Southern Africa’s tropical regions also led many African nomadic groups to settle down and start cultivating the land. The newly adopted agricultural lifestyle resulted in significant social and demographic changes within the Banana producing regions.

Citrus in the Mediterranean

Many citrus fruits originated across South and Southeast Asia. Over the centuries, they slowly made their way toward the Mediterranean. Citron and lemons were some of the first citrus fruits available in the area around the Mediterranean. Elite classes enjoyed them during the Roman empire. In the 10th century, the Middle Eastern Islamic world’s interconnectedness helped spread sour oranges and limes from Asia throughout the Mediterranean. By the 15th century, sweet oranges cultivation also had begun in the Mediterranean. 

Disease Transferred Through Trade Routes

Like commercial goods, culture, animals, and plants, disease transmits across exchange networks. The effects of this disease transfer have resulted in enormous changes throughout history.

The Black Death

One of the most consequential disease transfers in history began in the 14th century during Eurasia’s unification under the Mongol Empire. Increased interactions during this period led to the spread of the Black Death by plague-carrying fleas infected with the bacteria yersinia pestis. The fleas would jump onto rats that would then carry and disperse the fleas across vast areas. The fleas would then jump from the rats to people that they would bite, spreading the bacteria. The rats infected with plague fleas spread from China to Europe through international commercial networks. Estimates date the start of the plague in East Asia around the mid to late 1330s. By 1346 it had reached Europe. The main route of transmission was the Silk Roads. But it also spread through the Indian Ocean and Mediterranean Sea trade routes. The worst of the plague lasted until 1350.

Effects of the Black Death


The spread of the bubonic plague across Afro-Eurasia had enormous consequences. In Europe, between 1346 and 1348, upwards of 50% of the population died. The death rates across other regions were also high, including in China and the Islamic territories. The plague killed up to an estimated 200 million people out of a global population estimated to have been 375 million and 425 million. The following are two of the significant consequences of the spread of the bubonic plague. 

  • In Central Asia, which suffered greatly from the plague, what remained of Mongol power collapsed. The Mongol Yuan dynasty in China collapsed in 1351, a little over 15 years after the epidemic first appeared in China. 
  • Central Asian nomadic tribes also weakened to the point that the settled agricultural societies on their borders could begin exerting control within their territories. The power within central Asia switched decisively from nomadic groups to settled farming societies. 
  • In Europe, the nobility’s power weakened as the price of grain grown on the nobility’s land dropped in value. With so many dead, the value of labor increased, leading to improvements in the lowest classes’ living and working conditions as workers demanded better working conditions and work contracts. 
  • In Europe, people began to question the role and power of the Catholic church. People wondered why God would inflict the world with such a terrible disease if the church was in God’s good graces and the church spoke for God.