2.6 Environmental Effects of Trade

TLDR

Trade networks across Afro-Eurasia from about 1200 to 1450 spread more than goods. They moved crops like bananas, new rice varieties, and citrus that boosted food supplies, and they also carried diseases like the bubonic plague along the same routes. For AP World History, the core idea is that more connectivity caused real environmental and biological change, both helpful and devastating.

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One Environmental Consequence of Trade from 1200 to 1450

One environmental consequence of trade from 1200 to 1450 was the diffusion of crops across Afro-Eurasia. Bananas spread in Africa, new rice varieties spread in East Asia, and citrus spread in the Mediterranean, changing diets, farming, and population growth.

Another major consequence was the spread of pathogens along trade routes, especially the bubonic plague. For AP World, connect the cause and effect clearly: larger trade networks moved crops and diseases, which changed environments, populations, and societies.

Why This Matters for the AP World History Exam

This topic gives you clear evidence for causation questions: connected trade routes led directly to the spread of crops and pathogens. That cause-and-effect link is exactly the kind of reasoning the exam rewards.

You can use these examples to:

• Support arguments about the effects of trade networks like the Silk Roads, Indian Ocean routes, and trans-Saharan trade.
• Show both positive effects (new food crops) and negative effects (epidemic disease) of increased connectivity.
• Connect environmental change to social and economic change, such as population growth or labor shortages after the plague.

The required content here is short: crops and pathogens, including the bubonic plague, spread along trade routes. The named crop examples are bananas in Africa, new rice varieties in East Asia, and the spread of citrus in the Mediterranean. Other diseases, animals, and landscape effects are useful background, but treat them as supporting examples rather than required content.

Key Takeaways

• Trade routes spread both crops and pathogens across Afro-Eurasia between roughly 1200 and 1450.
• Bananas (from Southeast Asia) supported larger populations in African forest regions.
• Faster-growing rice varieties like Champa rice allowed multiple harvests and fueled population growth in East Asia.
• Citrus spread across the Mediterranean, aided by irrigation and farming knowledge in Muslim-ruled regions.
• The bubonic plague (Black Death) traveled along trade routes and killed a huge share of the population in affected regions.
• Connectivity caused environmental and biological change, not just cultural and economic change.

The Spread of Crops and Food Plants

As merchants and migrants moved across Afro-Eurasia, they carried useful plants with them. New food crops changed diets, farming practices, and even landscapes where they took hold.

Bananas in Africa

Bananas, originally from Southeast Asia, continued to spread and gain importance across parts of Africa during this period. They produced more calories per acre than many traditional crops and grew well in tropical forest regions where grains struggled.

That food security mattered. In forest regions, communities could support larger populations, and the surplus helped some groups build more complex political and trading systems. Banana cultivation spread gradually from East Africa into Central African rainforests, carried by traders and migrants.

New Rice Varieties in East Asia

Rice had been grown in East Asia for thousands of years, but faster-growing varieties boosted production sharply. Champa rice, originally from Vietnam, matured in about 60 days instead of 100 or more, tolerated drier conditions, and let farmers plant two or even three crops a year.

The effects were large:

• Food production rose, especially during China's Southern Song dynasty.
• Population grew as more food became available.
• Cities expanded because fewer farmers could feed more people.
• Farming pushed into hilly areas using new terracing and irrigation.

Citrus in the Mediterranean

Citrus fruits like lemons and oranges, also originally from Southeast Asia, spread across the Mediterranean. Farming knowledge and irrigation techniques in Muslim-ruled regions such as Sicily and Spain helped citrus grow in drier climates.

Citrus added vitamin C to local diets, could be preserved for year-round use, and became a profitable crop near trading ports. As Christian kingdoms took over former Muslim territories in Spain and Sicily, they kept and expanded citrus cultivation, so oranges and lemons were common across southern Europe by 1450.

Spread of Disease and the Black Death

The same networks that carried helpful crops also moved deadly pathogens. The clearest example is the bubonic plague, which caused the pandemic known as the Black Death.

The Black Death

The bubonic plague became the deadliest pandemic of the pre-modern world in the 1340s. It likely began in Central or East Asia and then spread along established trade routes.

How it moved:

• Along the Silk Roads from Central Asia toward the Black Sea region.
• By ship from Black Sea ports throughout the Mediterranean.
• Into European port cities on merchant vessels.
• Overland into the Middle East and North Africa.

The plague spread through fleas carried by rats that traveled on ships and in caravans, reaching populations with no built-up resistance.

The effects were severe:

• Some regions lost a large share of their population, with cities hit especially hard due to crowding.
• Some villages were abandoned, and trade temporarily collapsed in many areas.
• Labor shortages afterward pushed up wages for surviving workers.
• The death toll strained social structures and religious institutions, and traditional medical remedies failed to stop it.

Other Disease Exchanges (Supporting Context)

The Black Death was the most dramatic case, but it was not the only disease that moved along trade and migration routes. Illnesses traveled with merchant communities, military campaigns, pilgrims, and refugees. Previously isolated populations often suffered most, since they had little prior exposure. In response, some regions developed quarantine practices, especially after the plague.

Treat these broader disease exchanges as supporting context. The required example for this topic is the bubonic plague.

Environmental Effects Beyond Crops and Disease (Supporting Context)

Increasing connections had other environmental consequences worth knowing as background, though they are not the required content for this topic.

• Animals moved with traders, such as horses imported into India and Southeast Asia.
• New crops and farming pushed forests to be cleared and hillsides to be terraced.
• Growing trade strained resources, with timber cut for shipbuilding and fuel wood used for metalworking.

These details help you explain why connectivity reshaped landscapes, but for this topic, focus your required evidence on the diffusion of crops and pathogens.

How to Use This on the AP World History Exam

Multiple Choice

Expect documents or prompts about trade routes paired with questions about effects. If a source describes goods, merchants, or travel along the Silk Roads, Indian Ocean, or trans-Saharan routes, be ready to connect that movement to the spread of crops or disease.

Free Response

For causation prompts, use this clean chain: expanded trade networks moved people and goods, which spread crops and pathogens, which then changed populations and societies. Strong responses pair a benefit (new food crops supporting population growth) with a cost (plague causing massive death and labor shortages).

For continuity and change prompts, point out that biological exchange along trade routes was a long-running pattern, but the scale of the Black Death marked a sharp change in this period.

Using Sources Effectively

When you read a source about food, farming, or disease, ask how trade made that spread possible. Tie the specific item back to a route or region so your evidence is precise instead of vague.

Common Trap

Do not treat all environmental effects as equal. The exam wants you to recognize both helpful effects (crops) and harmful effects (disease) and explain the cause behind them, not just list random changes.

Common Misconceptions

• Bananas, rice varieties, and citrus were not invented in their new regions. They spread there from elsewhere, mainly Southeast Asia, through trade and migration.
• The Black Death did not appear randomly. It spread along existing trade routes, which is the whole point of this topic.
• The plague spread through fleas on rats, not through "bad air" alone, even though people at the time often blamed other causes.
• Trade effects were not only economic and cultural. They were also biological and environmental, which is exactly what this topic asks you to explain.
• New food crops were a real benefit, but they were not risk-free. The same connectivity that moved crops also moved disease.

Related AP World History Guides

• Unit 2 Overview: Networks of Exchange
• 2.1 The Silk Roads
• 2.3 Exchange in the Indian Ocean
• 2.4 Trans-Saharan Trade Routes
• 2.2 The Mongol Empire and the Making of the Modern World
• 2.7 Comparison in Trade from 1200-1450