This study examines the role of religion in ethnic nationalism and revolutionary wars between 1945 and 2001 using the Minorities at Risk (MAR) and State Failure (SF) datasets. It asks whether religion is an important factor in conflict and whether the level of this importance has changed over time. Few previous quantitative studies on religion and conflict analyze data from earlier than 1980. The analysis of the MAR dataset shows that until 1980 religious and non-religious ethnic nationalism caused a near-identical amount of conflict, but from 1980 onward, religious nationalist ethnic groups were responsible for increasingly more violent conflicts in comparison to non-religious nationalist groups. The analysis of the SF dataset shows a rise in religious violence beginning around 1965. The earlier date in the analysis from the SF dataset is attributed to the higher sensitivity of that dataset to changes in the level of violence. These results have several implications. First, they show that religion can influence conflict, but it is not the only influence. Second, the influence of religion on conflict can change over time. Third, religion's influence on conflict has been increasing. This contradicts modernization theory and secularization theory, which were the dominant paradigms in the Western social sciences for most of the 20th century and predicted the demise of religion as a relevant political and social force in the modern era.