Answer: separate themselves from those who were unlike them.
Nationalism is a political system that is characterized by the promotion of interests of a particular nation, especially to gain and maintain sovereignty. Moreover, nationalism is oriented towards developing and maintaining a national identity based on social characteristics such as culture and language.
The concept originated in the 18th century, and encouraged an attachment beyond family and native land. At the same time, it led people to want to separate themselves from those that were different from them.