Final answer:
European colonialism is the process that best describes the similarities between 18th century America and 20th century Africa, as it led to the colonization and exploitation of both continents by European powers.
Therefore, the correct answer is: option b). European colonialism
Step-by-step explanation:
European colonialism involved the expansion of European countries into other continents, with the Americas and the African continent being heavily colonized by European powers in their respective eras.
The colonization led to significant changes in the balance of power and saw the exploitation of natural materials and indigenous populations.
During the 18th century, European colonialism was manifested in North America through the establishment of colonies and the transatlantic slave trade.
Similarly, in the 20th century, nearly all of Africa fell under European control with colonial powers establishing their rule and exploiting the continent's resources. This period of colonial expansion significantly shaped the histories and economies of both continents.