Final answer:
Vasco de Gama's invasion of the Swahili city-states had a negative impact on the region, leading to a decline in trade and conflicts over religion.
Step-by-step explanation:
The invasion of the Swahili city-states by Vasco de Gama had a significant effect on the region. The Portuguese took advantage of the unfortified ports and looted and sank the ships of rival traders, which led to a decline in trade. Many merchants left the region, causing further economic impact. Additionally, the Portuguese attempted to convert the population to Roman Catholicism, resulting in conflict with the local African chiefs.