The geographic theme that is demonstrated by giving nicknames to states or countries is the human-environment interaction.
In this case, the fact that humans give nicknames to the states and countries shows us how the social experiences of the inhabitants of each of these places develops a transformation from the place of habitation to a place of belonging and community, where the nickname granted refers to the affective closeness and permanence of these people with those states and countries.
In synthesis, it shows us how human perception modifies something as essential as the name of a certain territory.