Which of the following is an example of nationalism?

a. a leader calls on his country's allies to protect his country from a threat posed by another country.

b. under an alliance, one country promises to defend another country from an attack by a third.

c. one country declares war on another country after that country attacks the first country's ally.

d. an activist organizes a protest of ethnic minorities in a country to demand that they be given their own country.