Europeans couldn't travel into the interior of Africa in order to take it over because of the African-ruled trade, couldn't navigate violent rivers, or overpower their strong armies. Disease also held them back.
It is noted that now 27 countries of the world peg their currencies to EURO. So the answer is EURO.
A historian using the historical thinking skill of examining historiography might try to determine how much has already been written about a certain subject before embarking on his or her own project, since this historiography of a topic can help you understand the evolution of "thinking about" the issue.
