Final answer:
The Portuguese changed the Indian Ocean trade network through their exploration, establishment of trading posts, and monopolization of the spice trade.
Step-by-step explanation:
The Portuguese significantly changed the Indian Ocean trade network through their exploration and establishment of trading posts. They demanded ships to carry a cartaz, a document with the Christian cross, in order to increase commerce for Portuguese merchants and generate revenue for the Portuguese government. The Portuguese also established trade networks along the coast of West Africa, trading for gold and slaves, and dominated the Swahili coast in East Africa, resulting in a decline in trade. Additionally, they expanded trade networks in Asia, monopolizing the spice trade and establishing ports in Goa, Macau, and Malacca.