Trade routes didn't just carry silks and spices—they transported living things that transformed environments across Afro-Eurasia. Between 1200 and 1450 CE, as caravans crossed deserts and ships sailed distant seas, they carried seeds, plants, animals, and unfortunately, disease-causing microorganisms. These biological exchanges had profound and lasting effects on human societies and natural environments. Some of these transfers, like new food crops, brought tremendous benefits. Others, like the devastating bubonic plague, caused immense suffering. Together, they show how greater connectivity changed not just human cultures but the natural world as well.
The Spread of Crops and Food Plants
As merchants traveled across Afro-Eurasia, they brought useful plants with them. New food crops changed diets, farming practices, and even landscapes in the regions where they were introduced.
Bananas in Africa
Bananas transformed agriculture and diet across much of Africa after their introduction from Southeast Asia. Though they had arrived in East Africa before this period, they continued to spread and gain importance between 1200 and 1450.
Bananas offered several advantages to African farmers:
- They produced more calories per acre than most traditional African crops
- They grew well in tropical forest regions where other crops struggled
- They could be harvested year-round, providing a steady food supply
- Different varieties could be eaten fresh, cooked, or made into beer
- They required less labor than grain crops once established
The impact of bananas on African societies was significant and far-reaching. Villages in forest regions could now support larger populations thanks to this productive crop. Banana cultivation spread gradually from East Africa into the Central African rainforests, carried by traders and migrants.
In forest regions from Uganda to the Congo Basin, bananas became dietary staples. Communities developed specialized cultivation techniques suited to local conditions. The increased food security provided by banana cultivation allowed some forest communities to develop more complex political organizations and trading networks.
A Portuguese explorer visiting the kingdom of Kongo in the 15th century noted: "These strange fruit they call 'banana' grow abundantly here, requiring little care once planted. The natives prepare them in many ways—roasted, boiled, and dried—and claim that a small plot with these plants can feed a family throughout the year. They guard their banana plants as carefully as we might guard a vineyard in Portugal."
New Rice Varieties in East Asia
Rice had been grown in East Asia for thousands of years, but the introduction of new, faster-growing varieties during this period significantly boosted food production. These new types of rice spread primarily from southern China into Korea, Japan, and other parts of East Asia.
Champa rice, originally from Vietnam, brought several benefits to farmers:
- It matured in just 60 days (compared to 100+ days for older varieties)
- It could be grown in drier conditions with less irrigation
- Farmers could plant two or even three crops each year instead of just one
- It was more resistant to drought and certain pests
- It could grow in higher elevations where traditional rice varieties couldn't thrive
The introduction of these improved rice varieties had profound effects on East Asian societies:
Food production skyrocketed, especially during China's Southern Song dynasty. The population grew dramatically as more food became available. More people could live in cities since fewer farmers could produce more food. Government tax revenue increased as rice harvests grew larger. Agricultural expansion moved into hilly areas previously considered unsuitable for farming.
By allowing multiple harvests per year, these new rice varieties also created changes in seasonal labor patterns. Farmers developed new irrigation systems and terracing techniques to maximize production of these valuable rice strains. Regional trading networks expanded to move surplus rice from productive areas to cities and less fertile regions.
Citrus in the Mediterranean
Citrus fruits—including lemons, oranges, and bitter oranges—spread throughout the Mediterranean region during this period, fundamentally changing both agriculture and cuisine. Originally from Southeast Asia, these fruits had moved gradually westward for centuries.
Muslim agricultural practices helped spread citrus across the Mediterranean:
- Islamic agricultural texts included detailed instructions for citrus cultivation
- Sophisticated irrigation systems made citrus growing possible in drier regions
- Muslim-ruled Sicily and Spain became major centers of citrus production
- Specialized gardens called "paradises" featured oranges as ornamental and food plants
- New grafting techniques allowed for better fruit quality and adaptation to local conditions
Citrus fruits brought multiple benefits to Mediterranean communities:
The fruits added valuable vitamin C to local diets, improving nutrition and health. Preserved lemons and oranges could be stored for use throughout the year. Citrus oils and extracts were used in perfumes and medicines. Citrus orchards became profitable commercial enterprises, especially near trading ports. The fruits inspired new culinary traditions that are still central to Mediterranean cooking today.
As Christian kingdoms conquered Muslim territories in Spain and Sicily, they maintained and expanded citrus cultivation. By 1450, oranges and lemons were common in gardens throughout southern Europe. The distinctive scent of orange blossoms became associated with regions like Valencia and Sicily, where orchards transformed both the landscape and the economy.
Spread of Disease and the Black Death
While the exchange of crops brought many benefits, the same networks that carried useful plants also transmitted deadly pathogens. The most devastating example was the bubonic plague, which caused the pandemic known as the Black Death.
The Black Death Pandemic
The bubonic plague erupted into the deadliest pandemic of the pre-modern world in the 1340s. It likely originated in Central or East Asia before spreading rapidly along trade routes.
The disease moved along established trade networks:
- It traveled the Silk Roads from Central Asia to the Black Sea region
- From Crimean ports, it spread by ship throughout the Mediterranean
- Merchant vessels carried it to European port cities
- Overland trade routes spread it into the Middle East and North Africa
- It even reached as far as sub-Saharan Africa along caravan routes
The plague was caused by the bacterium Yersinia pestis, carried by fleas that lived on rats. As infected rats traveled on ships and in caravans, they brought the disease to new populations with no immunity.
The pandemic's impact was catastrophic and wide-ranging:
- Between 1346 and 1353, it killed an estimated 75-200 million people
- Some regions lost 30-60% of their entire population
- Cities were especially hard-hit due to crowded conditions
- Some villages and small towns were completely abandoned
- Trade temporarily collapsed in many regions as people feared contact
The Black Death transformed societies across Afro-Eurasia:
Labor shortages after the plague led to higher wages for surviving workers. The massive death toll weakened traditional social structures and religious institutions. Some regions took decades or even centuries to recover their pre-plague population levels. Religious explanations for the disaster ranged from divine punishment to poisoning by marginalized groups. Medical theories and practices were questioned as traditional remedies failed to stop the disease.
Other Disease Exchanges
While the Black Death was the most dramatic example, other diseases also spread along trade routes during this period, though with less severe consequences.
Various diseases moved between regions:
- Smallpox spread along trade routes in Africa, affecting new populations
- Measles moved into previously isolated communities as trade connections grew
- Influenza strains traveled with merchants and diplomats
- Malaria expanded its range as agricultural patterns changed
- Waterborne diseases spread through growing urban centers connected to trade
Disease exchanges often accompanied human migration:
- Merchant communities carried diseases between trading cities
- Military campaigns spread illnesses between regions
- Pilgrimages to religious centers became vectors for disease transmission
- Refugees fleeing conflicts or environmental disasters carried pathogens to new areas
- Growing cities attracted migrants who brought unfamiliar diseases
The impacts of these disease exchanges varied:
- Previously isolated populations often suffered most severely
- Some diseases became endemic (constantly present) in newly affected regions
- Knowledge of treatments sometimes followed disease pathways
- Quarantine practices developed in some areas, especially after the Black Death
- Trade sometimes declined temporarily when disease outbreaks occurred
Environmental Impacts Beyond Crops and Disease
The increasing connections across Afro-Eurasia had other environmental consequences beyond the movement of crops and diseases.
Animal species moved along with human travelers:
- Horses from Central Asia were imported to India and Southeast Asia
- New cattle breeds spread through trade corridors
- Sheep varieties moved between different pastoral regions
- Domesticated animals sometimes escaped to become invasive species
- Animal diseases followed similar paths to human diseases
Landscape changes accompanied the spread of new crops:
- Forests were cleared for expanding agriculture
- Irrigation systems altered water flow patterns
- Terracing transformed hillsides for farming
- Urban growth around trading centers changed local environments
- Mining for trade goods scarred landscapes and polluted waterways
The intensification of trade sometimes led to resource depletion:
- Valuable timber was harvested for shipbuilding
- Fuel wood was consumed in growing quantities for metalworking
- Overgrazing occurred along major caravan routes
- Some luxury goods (like certain spices or animals) became harder to find
- Water resources were strained around major urban centers
The environmental exchanges of the period between 1200 and 1450 CE demonstrate how human connections can have far-reaching ecological consequences. The movement of plants, animals, and microorganisms across traditional boundaries created new environmental relationships that continue to shape our world today. These exchanges—both beneficial and harmful—remind us that globalization has deep historical roots and profound environmental dimensions.
Vocabulary
The following words are mentioned explicitly in the College Board Course and Exam Description for this topic.
| Term | Definition |
|---|---|
| Afro-Eurasian trade | Commercial networks and exchange of goods connecting Africa, Europe, and Asia, facilitated by imperial expansion and conquest. |
| bubonic plague | A devastating epidemic disease transmitted along trade routes that caused massive mortality in Afro-Eurasia during the medieval period. |
| diffusion of crops | The spread and adoption of plant species across different regions through trade networks and cultural exchange. |
| diffusion of pathogens | The transmission and spread of disease-causing organisms across regions through trade routes and human contact. |
| epidemic diseases | Diseases that spread rapidly through a population, affecting large numbers of people across wide geographic areas. |
| networks of exchange | Interconnected systems of trade and cultural interaction spanning vast distances, developed during the period c. 1200 to c. 1450. |
Frequently Asked Questions
What are the environmental consequences of connectivity from 1200 to 1450?
From 1200–1450, increased connectivity changed environments in predictable ways you should be able to explain for AP Topic 2.6 (Learning Objective K). Trade networks (Silk Roads, Indian Ocean, Trans-Saharan) spread new crops—Champa rice in East Asia, bananas in Africa, citrus around the Mediterranean—boosting food supplies, population growth, and changes in land use (more irrigation, wet-rice terraces). The Pax Mongolica and faster travel also moved pathogens: Yersinia pestis traveled along trade routes with black rats (Rattus rattus) and flea vectors, causing the Black Death and dramatic population decline that altered labor systems and reforested abandoned land. Climatic shifts like the Little Ice Age interacted with these changes, stressing agriculture. For the exam, be ready to link specific environmental effects (crop diffusion, epidemic disease) to particular networks and provide evidence—use examples above. More help: see the Topic 2.6 study guide (https://library.fiveable.me/ap-world-history/unit-2/environmental-effects-trade/study-guide/UCLw0VRGZlznG73u3F9o) and practice problems (https://library.fiveable.me/practice/ap-world-history).
Why did diseases spread so much along trade routes during this time period?
Because trade routes connected more places and people than before, pathogens moved with them. Caravans, merchant ships, and pilgrims carried not just goods but also infected people and animals. The Pax Mongolica made long-distance travel safer and faster across Eurasia, increasing contacts between cities. Flea-bearing rats (Rattus rattus) rode on ships and caravans; fleas transmitted Yersinia pestis (the bubonic plague) from rodents to humans. Dense port cities and caravanserais helped diseases jump quickly because lots of strangers lived close together, and weakened or malnourished populations had less resistance. Climatic shifts (like the Little Ice Age) and crop disruptions also made people more vulnerable. On the AP exam, use these causal links—trade networks + vectors (rats/fleas) + urban density + Pax Mongolica—to explain diffusion of epidemic disease (Topic 2.6). For review, check the Topic 2.6 study guide (https://library.fiveable.me/ap-world-history/unit-2/environmental-effects-trade/study-guide/UCLw0VRGZlznG73u3F9o) and practice questions (https://library.fiveable.me/practice/ap-world-history).
What's the bubonic plague and how did it spread through trade networks?
The bubonic plague (Black Death) was a deadly epidemic disease caused by the bacterium Yersinia pestis. It infected humans when flea vectors—often carried on black rats (Rattus rattus)—bit people, producing swollen “buboes,” fever, and high mortality. Between c. 1200–1450 the plague spread rapidly across Afro-Eurasia along trade routes: the Silk Roads, Indian Ocean shipping lanes, and trans-Saharan networks. The Pax Mongolica helped by making long-distance travel and caravan/ship safety more reliable, so infected rats and fleas rode merchant ships and caravans from Central Asia into Europe, North Africa, and the Middle East. On the AP exam this fits Topic 2.6 (environmental consequences of connectivity) and can show diffusion of pathogens—use terms like Yersinia pestis, Rattus rattus, flea vectors, Silk Roads, and Pax Mongolica. For a focused review, see the Topic 2.6 study guide (https://library.fiveable.me/ap-world-history/unit-2/environmental-effects-trade/study-guide/UCLw0VRGZlznG73u3F9o) and practice questions (https://library.fiveable.me/practice/ap-world-history).
How did new crops like bananas and rice varieties spread to different regions?
New crops spread mostly because people moved them along existing trade and migration networks. Austronesian sailors brought bananas and other tropical crops westward into the Indian Ocean and then to coastal East Africa; over centuries those plants took root in new ecologies and supported population growth. Champa rice (a fast-ripening, drought-resistant variety) spread from Champa/Vietnam into China via trade contacts and diplomatic exchanges along the South China Sea and overland routes, increasing rice yields and fueling urban growth. Merchants, migrants, and state-sponsored exchanges—not just accidental diffusion—carried seeds, grafting techniques, and farming knowledge across the Silk Roads, Indian Ocean routes, and Trans-Saharan links. For the AP exam, link these examples (bananas in Africa, Champa rice in East Asia) to Topic 2.6’s focus on environmental consequences of connectivity. For a concise review, see the Topic 2.6 study guide (https://library.fiveable.me/ap-world-history/unit-2/environmental-effects-trade/study-guide/UCLw0VRGZlznG73u3F9o) and practice questions (https://library.fiveable.me/practice/ap-world-history).
What were the main environmental effects of increased trade between 1200-1450?
Between 1200–1450 increased trade reshaped environments in a few big ways. First, crops spread widely: Champa rice boosted Chinese rice yields, bananas and other Austronesian crops transformed African diets and farming, and citrus moved around the Mediterranean—all increasing food variety and population growth. Second, trade moved pathogens: the bubonic plague (Yersinia pestis), carried by black rats (Rattus rattus) and flea vectors, traveled along Silk Roads, Indian Ocean, and Trans-Saharan routes, causing massive mortality and social disruption. Third, intensive agriculture and expanded irrigation to meet market demand changed landscapes and soil use. Finally, longer-term climate shifts like the Little Ice Age interacted with these changes, worsening harvest failures and migration. For the AP exam, this fits Learning Objective K—be ready to explain crop diffusion and epidemic spread using specific examples (see Fiveable’s Topic 2.6 study guide for review) (https://library.fiveable.me/ap-world-history/unit-2/environmental-effects-trade/study-guide/UCLw0VRGZlznG73u3F9o). For broader review, check Unit 2 (https://library.fiveable.me/ap-world-history/unit-2) and practice questions (https://library.fiveable.me/practice/ap-world-history).
I'm confused about how trade routes caused environmental changes - can someone explain this simply?
Trade routes changed environments in two big ways: moving species (plants, animals, pathogens) and increasing local resource use. As merchants and sailors carried crops like Champa rice, bananas, and new citrus varieties, regions’ diets and farming expanded—sometimes raising population but also pushing more land into rice paddies or orchards. Ships and caravans spread Yersinia pestis (the bubonic plague) via rats and fleas along the Silk Roads and Indian Ocean, causing demographic collapse that actually shifted land use afterward. Increased long-distance trade under the Pax Mongolica and booming markets also led to more deforestation, irrigation, and soil exhaustion near ports and trade cities. These changes are exactly what the CED wants you to explain for Topic 2.6 (e.g., Silk Roads, Indian Ocean, Trans-Saharan, bubonic plague, Champa rice). For a focused review, check the Topic 2.6 study guide (https://library.fiveable.me/ap-world-history/unit-2/environmental-effects-trade/study-guide/UCLw0VRGZlznG73u3F9o) and practice questions (https://library.fiveable.me/practice/ap-world-history).
What's the difference between crop diffusion and disease diffusion along trade routes?
Crop diffusion and disease diffusion both moved along the same networks (Silk Roads, Indian Ocean, Trans-Saharan) but differ in mechanism, speed, and effects. - Mechanism: crops spread intentionally (human migration, trade, agricultural adoption—e.g., Champa rice to China, bananas to Africa, citrus in Mediterranean), while diseases often spread unintentionally via biological vectors and trade traffic (e.g., Yersinia pestis carried by Rattus rattus and fleas). - Timescale & pattern: crops could be adopted gradually and transform local diets/ecologies; pathogens often caused rapid, episodic epidemics (the Black Death) with immediate demographic shocks. - Consequences: crop diffusion boosted food supply, population growth, and economic change; disease diffusion caused mortality, labor shortages, social disruption, and sometimes political/economic shifts. For AP exam use: connect examples to Topic 2.6 learning objective K and cite networks (Pax Mongolica increased connectivity). Review this topic on the Fiveable study guide (https://library.fiveable.me/ap-world-history/unit-2/environmental-effects-trade/study-guide/UCLw0VRGZlznG73u3F9o) and practice questions (https://library.fiveable.me/practice/ap-world-history).
How did bananas end up in Africa and why does this matter for AP World?
Austronesian sailors brought bananas to coastal East Africa (and Madagascar) by about the first millennium CE through Indian Ocean voyaging; those crops then spread inland with Bantu-speaking migrants and via Indian Ocean trade networks (keywords: Austronesian voyaging, Indian Ocean trade, bananas in Africa). That matters for AP World because it’s a clear example of crop diffusion changing environments and societies: bananas provided a high-yield, reliable food source that supported population growth, more permanent settlements, and intensified agriculture in the Great Lakes and other regions. For Topic 2.6 you should link the biological diffusion to environmental consequences (land use change, demographic shifts) and to broader networks like the Indian Ocean and Trans-Saharan exchanges. On the exam you might use this as evidence in short-answer or LEQ/DBQ questions about environmental effects of connectivity. For a tight review, see the Topic 2.6 study guide (https://library.fiveable.me/ap-world-history/unit-2/environmental-effects-trade/study-guide/UCLw0VRGZlznG73u3F9o) and Unit 2 overview (https://library.fiveable.me/ap-world-history/unit-2); practice questions are at (https://library.fiveable.me/practice/ap-world-history).
Why did citrus fruits spread around the Mediterranean during this period?
Citrus spread around the Mediterranean because long-distance trade and increased connectivity moved plants, people, and agricultural knowledge. Muslim merchants and travelers (working across the Indian Ocean and Silk Roads) reintroduced and promoted citrus varieties grown in South/Southeast Asia and the Arabian Peninsula. Trade networks (including ports and caravan routes) carried living plants, seeds, and grafting techniques; irrigation and new farming methods made citrus cultivation possible in Mediterranean climates. Demand for fresh fruit, medicinal uses, and luxury/status consumption also encouraged farmers to adopt citrus. This fits the CED’s idea of “diffusion of crops” through Afro-Eurasian networks (Topic 2.6). For quick review of these connections and exam-style practice, check the Topic 2.6 study guide (https://library.fiveable.me/ap-world-history/unit-2/environmental-effects-trade/study-guide/UCLw0VRGZlznG73u3F9o) and try practice questions (https://library.fiveable.me/practice/ap-world-history).
What were the consequences of new rice varieties spreading in East Asia?
New, fast-maturing rice varieties (like Champa rice) spread through East Asia and had big environmental and social effects. Agriculturally, they let farmers double-crop—more than one harvest per year—which raised yields and supported rapid population growth. That population increase fueled urbanization, labor specialization, and state building. Environmentally, expanding rice paddies required more irrigation, led to conversion of wetlands and some deforestation, and intensified land use (which could cause local soil depletion and greater demand for water). Politically and economically, greater food surpluses supported bigger armies and bureaucracies and changed trade patterns. On the AP exam, use this as a causation example in short-answer or DBQ prompts about connectivity’s environmental impacts (Topic 2.6). For a quick review, see the Topic 2.6 study guide (https://library.fiveable.me/ap-world-history/unit-2/environmental-effects-trade/study-guide/UCLw0VRGZlznG73u3F9o) and practice questions (https://library.fiveable.me/practice/ap-world-history).
How do I write an essay about environmental effects of trade networks for the DBQ?
Start with a clear thesis that connects trade networks to specific environmental effects (crop diffusion, ecosystem change, disease spread) and place it in context (Pax Mongolica, expanded Silk Roads/Indian Ocean/Trans-Saharan contacts c.1200–1450). For the DBQ: use at least four documents to support your argument, describe broader context, and for two documents explain POV/purpose/situation. Bring one piece of outside evidence (e.g., spread of bubonic plague—Yersinia pestis via Rattus rattus and fleas along Silk Road routes; Champa rice boosting population and changing land use in East Asia; bananas and Austronesian diffusion in Africa). Organize paragraphs by causal theme (crop diffusion → agricultural change; trade → disease diffusion; new crops → demographic/ecological shifts). End by showing complexity (trade increased connectivity but had mixed environmental outcomes). For topic review and examples you can use the AP-aligned study guide (https://library.fiveable.me/ap-world-history/unit-2/environmental-effects-trade/study-guide/UCLw0VRGZlznG73u3F9o) and practice DBQ practice questions (https://library.fiveable.me/practice/ap-world-history).
Did the bubonic plague really spread because of increased connectivity and trade?
Yes—increased connectivity and trade were major reasons the bubonic plague (caused by Yersinia pestis) spread so widely in the 14th century. Networks like the Silk Roads and Indian Ocean routes, especially under the relative safety and stability of the Pax Mongolica, moved people, goods, and animals across Afro-Eurasia. Black rats (Rattus rattus) and their flea vectors hitched rides on merchant ships and caravans; when infected fleas bit humans, the disease jumped into populations along trade hubs and port cities. The CED highlights exactly this diffusion of pathogens along trade routes in Topic 2.6—it’s a classic example of environmental consequences of connectivity. For AP review, make sure you can connect trade networks (Silk Roads, Indian Ocean) to disease spread and use specific terms (Yersinia pestis, Rattus rattus, flea vectors). For a focused review, see the Topic 2.6 study guide (https://library.fiveable.me/ap-world-history/unit-2/environmental-effects-trade/study-guide/UCLw0VRGZlznG73u3F9o) and practice questions (https://library.fiveable.me/practice/ap-world-history).
What other epidemic diseases besides the plague spread along trade routes?
Besides the bubonic plague, several other epidemic diseases moved along Afro-Eurasian trade routes. Notable examples are smallpox and measles (highly contagious viral diseases that traveled with people and caravans), leprosy (dispersed via Indian Ocean and Silk Road contacts), and various respiratory illnesses like influenza. Vector-borne diseases such as malaria also spread more widely as human movement and ecological change accompanied trade. These disease flows fit the CED’s emphasis on “diffusion of pathogens” along the Silk Roads, Indian Ocean, and Trans-Saharan routes and are important to mention when explaining environmental consequences of connectivity (Topic 2.6). For quick AP review, check the Topic 2.6 study guide on Fiveable (https://library.fiveable.me/ap-world-history/unit-2/environmental-effects-trade/study-guide/UCLw0VRGZlznG73u3F9o) and practice questions (https://library.fiveable.me/practice/ap-world-history) to see how disease diffusion can be used as evidence on short-answer and essay prompts.
I missed class - what does "diffusion of crops and pathogens" actually mean?
"Diffusion of crops and pathogens" just means things spread from one region to another along trade networks. Crops: merchants, sailors, and migrants carried plants and farming techniques (e.g., Champa rice to China, bananas into Africa, citrus around the Mediterranean). Those new crops changed diets, population growth, and agricultural systems. Pathogens: people, animals (like Rattus rattus, the black rat), and fleas moved along the Silk Roads, Indian Ocean routes, and Trans-Saharan caravans, carrying diseases such as Yersinia pestis (the bubonic plague). Epidemics could sharply reduce populations and disrupt economies and societies. For the AP exam, be ready to explain causation and effects (how connectivity caused diffusion and the environmental/social consequences) in MCQs and SAQs/DBQs. For a quick review of Topic 2.6 and examples to use on the exam, see the Fiveable study guide (https://library.fiveable.me/ap-world-history/unit-2/environmental-effects-trade/study-guide/UCLw0VRGZlznG73u3F9o). For extra practice, Fiveable has 1,000+ AP practice questions (https://library.fiveable.me/practice/ap-world-history).
How did trade networks between 1200-1450 change the environment in different regions?
Between 1200–1450 expanding trade networks (Silk Roads, Indian Ocean, Trans-Saharan) changed environments by moving plants, animals, and pathogens across regions. New crops like Champa rice and bananas spread into China and Africa, boosting food supplies, population growth, and new land cleared for agriculture. Citrus moved around the Mediterranean, changing diets and orchard landscapes. The Pax Mongolica increased connectivity, helping faster diffusion—but it also helped pathogens: Yersinia pestis (the bubonic plague) traveled along caravan and ship routes, carried by Rattus rattus and flea vectors, causing massive mortality and labor shortages that altered land use (abandoned fields, reforestation) and contributed to climate-linked stress (Little Ice Age effects). These environmental changes are exactly what AP Learning Objective K asks you to explain. For focused review, see the Topic 2.6 study guide on Fiveable (https://library.fiveable.me/ap-world-history/unit-2/environmental-effects-trade/study-guide/UCLw0VRGZlznG73u3F9o) and practice dozens of related questions at Fiveable Practice (https://library.fiveable.me/practice/ap-world-history).