Unit 2 covers the three great exchange networks of 1200 to 1450 - the Silk Roads, the Indian Ocean, and the trans-Saharan routes - and asks the same question of each: what made trade grow, and what did that growth change?

Three useful explanations link a change to a trading obstacle; their relative importance varied by route and time:

• Improved commercial practices 商业惯例的改进 - money economies 货币经济, credit 信贷, and forms of partnership that spread risk.
• Improved transportation technologies 交通技术的改进 - better ships, saddles, and navigation.
• State support 国家支持 - empires that secured routes and taxed the trade benefited from protecting it.

Demand mattered too: luxury goods 奢侈品 from Chinese, Persian, and Indian artisans found expanding markets across Afro-Eurasia, and producers increased output to meet that demand.

The Silk Roads 丝绸之路 carried high-value, low-bulk goods overland across Eurasia: silk, porcelain, spices, and precious metals.

Its enabling innovations were commercial as much as technical - caravanserai 商队旅馆 along the routes, the use of paper money 纸币 and bills of exchange 汇票 in China, and forms of credit that let merchants trade without carrying bullion.

Demand for exports encouraged Chinese, Persian and Indian producers to expand textiles and porcelain production; iron and steel manufacture also expanded in China. Trading cities such as Kashgar 喀什 and Samarkand 撒马尔罕 gained from the flow of merchants and goods. These routes existed before 1200: the change was expansion and intensification, not their invention. A caravanserai supplied lodging and a place for exchange; credit reduced the need to transport all payment as precious metal.

The Mongol Empire 蒙古帝国 expanded through organised military force, including effective cavalry tactics, as rival states weakened or fragmented. Conquest displaced populations and overthrew rulers. Successor khanates 汗国, including Yuan China and the Ilkhanate in Iran, developed distinct political and cultural settings; the whole network did not remain one uniformly peaceful state throughout 1200–1450.

Mongol expansion facilitated Afro-Eurasian trade and communication by linking large territories, incorporating new peoples and supporting travel and communications. A relay system helped official messages move; protection and trade-friendly practices could reduce travel risks. The term Pax Mongolica 蒙古和平 describes this period of facilitated connections, not universal peace.

Interregional contacts and conflicts also encouraged technological and cultural transfers: gunpowder technology moved west, knowledge and crafts circulated, and scholars and craftsmen were relocated across the empire. The adoption of Uyghur script and the circulation of Greco–Islamic medical knowledge illustrate transfers; local traditions also influenced Mongol rulers. Some rulers adopted their subjects’ religions or tolerated varied practices to support legitimacy.

Political violence and increased connections could coexist. Explain the particular effect a prompt asks about; destruction and exchange do not automatically cancel each other, and not every response needs both.

The Indian Ocean network moved bulkier goods than the Silk Roads - textiles, timber, grain, and spices - because ships could carry larger cargoes at lower transport cost per unit. This is a relative tendency, not a rule that maritime trade carried only cheap bulk goods: luxury goods also travelled by sea.

Seasonally changing monsoon winds 季风 helped merchants plan outward and return voyages. Environmental knowledge worked with larger ship designs, the lateen sail 三角帆, vessels such as the dhow 单桅帆船, and navigational tools including the compass 罗盘 and astrolabe 星盘. The compass helped indicate direction and the astrolabe supported celestial observations. These tools improved navigation; they did not make winds irrelevant or every voyage safe.

Important effects included:

• The network fostered the growth of states, such as the Swahili city-states on the East African coast, Gujarat and the Sultanate of Malacca.
• Merchants established diasporic communities 侨居社群 in key ports, introducing their own culture while adopting local ways. Arab and Persian communities in East Africa and Chinese merchant communities in Southeast Asia are examples. Cultural change could operate in both directions.
• The movement of people included free merchants and coerced labour; trade was not uniformly free or voluntary. Do not treat every merchant or sailor as enslaved.

Ming voyages led by Zheng He 郑和 illustrate state-sponsored maritime connections in the early fifteenth century. They encouraged diplomatic and cultural contacts across existing Indian Ocean networks, rather than creating those networks from nothing.

The trans-Saharan routes crossed the desert on innovations in existing technology - above all the camel saddle 骆驼鞍 and organised caravans 商队.

Gold from West Africa moved north and salt 盐 moved south. The expansion of empires, including Mali 马里帝国, facilitated Afro-Eurasian trade by securing the routes and taxing them - and Mansa Musa 曼萨·穆萨’s pilgrimage demonstrated Mali’s wealth and connections to the Islamic world. Desert transport and state activity interacted; a camel saddle alone does not explain the entire growth of a trading empire.

Increased cross-cultural interaction produced diffusion 传播 of literary, artistic, scientific, and religious traditions - the spread of Islam along trade routes, Buddhist influence in East Asia and Hindu and Buddhist influence in Southeast Asia, and the movement of scientific and mathematical knowledge.

Travellers 旅行者 such as Ibn Battuta 伊本·白图泰, Marco Polo 马可·波罗 and Margery Kempe wrote accounts as connections intensified. Such accounts are evidence to interpret: ask about the writer’s purpose, audience, viewpoint and access to information. A traveller’s description does not automatically represent every person or place.

The fate of cities varied: some declined as routes shifted or invasions came, while others grew into major commercial centres.

The environmental consequences were as large as the cultural ones. Continued diffusion of crops and pathogens linked environmental change to exchange. Examples include bananas in Africa, new rice varieties in East Asia and citrus around the Mediterranean. Crops could support agricultural production and population growth where local conditions allowed. Epidemic disease also moved through connections: the Black Death 黑死病 spread across connected regions in the fourteenth century and caused severe mortality. Effects varied; neither an absence of all prior immunity nor a fixed death rate for all Afro-Eurasia follows from the syllabus. City decline could reflect epidemic disease, warfare or changing routes; urban growth could reflect productivity and trade. Do not turn these separate processes into an inevitable four-step sequence.