Answer
a) The author uses Social Darwinism to justify imperialism in the passage. He argues that the weak must be devoured by the strong, and that it is the natural law of beneficent nature. This ideology was used to justify the domination of one race over another, and it was believed that the superior race had the right to rule over the inferior race.
b) The historical situation of the late nineteenth century, which was characterized by intense competition among European powers for colonies and resources, might have affected the vision of Africa's future outlined by the author in the third paragraph. The author's vision of Africa's future is based on the assumption that European powers will continue to dominate and exploit Africa, and that Africa will become a playground for European noblemen and tourists. However, this vision ignores the possibility that African nations might resist European domination and exploitation, and that they might develop their own economies and societies.