The correct answer to this open question is the following.
How does separating people from interacting with each other create rivalries and distrust?
Rivalries and distrust are created because separated people need to compete to get the limited resources available. This competition has been taken to the extreme in the cases people fight with each other to exert power, control, and domain. This creates a sense of superiority in which one race, ethnicity, or social class believes has the right to impose its will over the others.
How might this relate to segregation along racial lines in society?
In that high social class think they have the right to exert their will just because they consider themselves superior. It could be because of their color of skin, their wealth, or social status. And they find ways to show it
What is xenophobia?
We understand xenophobia as the hatred one nation has over people from other countries. This sentiment has been the origin of racial segregation and wars.