Is humanity's circle of moral concern expanding, as often claimed? I explore frequencies of morally universal language in 15m book publications in American English, British English, French, Spanish, German, and Italian from 1800-2000. In each language, morally universal terminology diminished substantially. I then test two prominent hypotheses predicting moral universalism: reason and religion. Reason-based terminology correlates positively with morally universal and morally communal terminology, explaining seemingly contradictory observations of the 20th century. In contrast, communal terminology sub-sides when religious terminology becomes more frequent. These empirical patterns cast doubt on prominent claims of moral universalism expanding.