Which of the following is an example of nationalism?

A. Under an alliance, one country promises to defend another country from an attack by a third.

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

C. A leader calls on his countries allies to protect his country from a threat posed by a neighboring nation-state.

D. One country declares war on another power after that power invades the first countries ally.