["Nations and Nationalism, Volume 27, Issue 1, Page 238-259, January 2021. ", "\nAbstract\nSeminal contributions to the study of nation‐building emphasized the role of newspapers in the development of national consciousness. But do such theories apply in the modern context of online news sites, especially in diverse, postcolonial societies? Because online news sites contain forums for reader comments, this provides an opportunity to assess the relationship between exposure to media content and citizen sentiments. We investigate the extent to which a major online news site makes ethnic categories salient in sub‐Saharan Africa's largest country, Nigeria. Analysing more than 35,000 news articles and 300,000 comments, we find that commenters frequently broadcast strong expressions of subnational ethnic animus in response to a wide variety of stories. In particular, the use of some ethnic categories in headlines is associated with more than 40 percentage point increase in the probability of at least one reader making an ethnic‐based comment. Extending the analysis to South Africa, we show that these patterns generalize beyond Nigeria. By amplifying ethnic animus, ‘national’ newspapers may impede nation‐building efforts.\n"]