What word describes the fear of foreigners?

Xenophobia

According to the Oxford and Macmillan dictionaries. The term xenophobia can be understood as the fear of foreigners of a certain group of people with its defined culture and social rules by another group of people with different uses and customs.

Explanation:

Xenophobia is comprehended as the fear a certain individual or group might experience by observing or trying to conceptualize an individual or a group of individuals that don’t belong to their specific and defined social group. This applies to any kind of established group of people living in a certain way of uses and customs. In other words, any human settlement. That is why people from "Star City" can be xenophobic of people from "Ruby City" even if they are only 100 kilometers away from the other. The specific factor that awakens or triggers Xenophobia is the fear of different uses and customs of life.