I'm looking for a sutta which mentions nationalism
On this page, you can find Thanissaro Bhikkhu's summary for MN 93:


  The Buddha enters into a debate with a brahman on whether one's worth
  as a person is determined by birth or by behavior. Although some of
  the arguments he presents here deal with the specifics of brahman
  caste pride, many of them are applicable to issues of racism and
  nationalism in general.