Final answer:
Portuguese explorers found highly evolved Eastern African coastal societies with wealth from trading items like gold and ivory and established trade relations to gain resources and slaves.
Step-by-step explanation:
When Portuguese explorers reached the Atlantic coast of central and southern Africa, they found highly evolved societies and vast wealth. These Eastern African coastal societies were engaged in trading various items, including gold, ivory, and slaves.
The Portuguese were driven by their desire for wealth and religious motives, aiming to find an oceanic route to Asia, bypass the Muslim-held trans-Saharan trade routes, and gain access to African resources. They established citadels such as the fortress of Elmina and entered into relations with African kingdoms such as Benin and Kongo, leading to a close connection with Kongo.
This connection aided the Portuguese in obtaining slaves for their trade endeavors. Moreover, they marveled at the wealth of the city-states they encountered and took advantage of existing trading networks, subsequently establishing colonies and introducing Catholicism in regions like Kongo.