What are countries trying to accomplish with imperialism?

Consider this case study - the Zulu empire grew out of a change in the culture. There came into being a requirement that a young man, to take a wife, must first kill an enemy man. Cows were also important symbols of wealth, and required land to graze. These two cultural imperatives grew until the Zulu nation, originating in central Africa, slaughtered its way east and south, until they finally reached what is now South Africa. It's estimated that they killed at least 10 percent of the African population on their long migration.

In South Africa, they met implacable foes - the Boers and the British. The more numerous Zulus were fought to a standstill by the