These are examples of possible types of searches. They are not intended to define in any way the limits of searching for this topic. The second search. for example, is for one nation. There is significant immigration associated with quite a few of the 54 nations on the African Continent. One could conduct a similar search using the name of any African nation of interest. Although, there is guarantee that such a search will generate hits. The third search is for J. Crush, who was written about this topic. Of course, any relevant author might be substituted for Crush.