How did the Columbian Exchange affect the Americans? How did it affect Europe, Asia, and Africa?

What would lead a historian to consider two events to have a relationship of correlation rather than causation

Match the events to the impact they had on africa during the late 19th century 1.colonization of the congo 2.berlin conference of 1884 3.berlin act of 1885 settled tutorial disputes between european nations prohibited the slave trade in africa marks the beginning of scramble for africa

What was the most important consequence of the large-scale ecological changes in africa two hundred thousand years ago?