The correct answer is B) separate themselves from those who were unlike them.
Nationalism encouraged people with a shared identity to separate themselves from those who were unlike them.
Nationalism implies people that have a special love, passion, or devotion for their country, customs, history, culture, and tradition. This ideology just promotes the interests of the nation and do not like outer interventions or people from different countries, ideas, and background. Nationalists do not like to mingle with other nationalities.
The other options of the question were A) declare war on all those who did not share their beliefs, C) be open to other peoples' traditions, and D) convince other people to share their common bonds.