What were the causes of European Imperialism in Africa during the period 1750-1914?

I concur with the above answer, and would also like to add
a couple of other factors that influenced Imperialism in Africa during this time
period.

Strategic Advantage -
First, consider the strategic significance of African colonies such as
South Africa and Egypt, which gave Britain control of vital waterways for trade routes
in the Cape of Good Hope and later, in the Suez Canal and the Mediterranean Sea.  This
allowed the British Empire to maintain its dominance of the high seas, especially during
the time period you mention.  These trade routes, it should be said, made imperialism in
Asia and the Middle East more feasible
too.

Cultural Imperialism -
Underlying the desire of these countries to spread their empires was the racist and
arrogant belief that their empires, cultures, languages and religions were also superior
to the tribes and peoples of Africa, and that taking their natural resources could be
justified by "civilizing" such peoples.