The answer is: A. world war I
One of the major characteristic of modernist writers is their realistic view on human nature that might cause a certain society to behave in 'inhumane' way. This provide a perception that people who are seen as 'evil' by a certain group might not be seen as son by another group.
World War I depict the clash with several nations that had their own reasons/goals in joining the war. The writers at that time see that in order to committed to the war, each nations have to believe that their reasons are the one that is 'righteous' while other nations' reasons are the one that is 'wrong' or evil.