How can the effects of one migration become a cause of another migration?

Effects of one migration from one population can become a cause of another migration of another population because the new population can consume the resources of the land, forcing the old population to leave in search of new resources.

Ithink that the missing word is mixed

Africans learned what the europeans wanted them to learn. instead of learning about african history and current information that could and would them they learned solely what europe wanted them to. and not everyone received the same education, some received better and others none.