How ideology blinds scholarship

"...the sources relating to Dakota Territory... (reveal) the ubiquity of Christian symbols, structures, practice, and belief. Early-twentieth-century progressive historians, in contrast, did not take religion as a social force very seriously... Henry F. May commented that the ideology of progressive history included the 'assumption that religion was and must be declining.' Research on the history of religion in the United States in recent years has helped to emphasize its importance to earlier generations of Americans, as has a raft of books arguing that religious and ethnic factors were more important influences on the behavior of voters in the late nineteenth century than were economic concerns."