The first known use of the word “mainline” to describe the largest Protestant denominations and distinguish them from their growing evangelical and fundamentalist counterparts appeared in the New York Times in 1960””at the very moment when mainline Protestantism began its rapid decline. You don’t call something “mainline” or “mainstream” unless its supremacy is being disputed (think of the “mainstream media”). And the supremacy of older, more socially prestigious churches within American Protestantism was being directly disputed in the mid-1950s. It’s impossible to speak with precision about what constituted mainline Christianity, but in general the mainline churches de-emphasized doctrinal differences; were Northern and Midwestern rather than Southern; promoted social causes rather than personal conversion or repentance; and virtually always took the liberal line in politics. By 1960, liberal Protestantism enjoyed almost nothing of the authority that had seemed unassailable 15 years earlier.
In “The Christian Century and the Rise of the Protestant Mainline,” Elesha Coffman charts the half-century ascendancy of liberal Protestantism in American society from its beginnings in northern seminaries at the turn of the 20th century to its brief triumphant moment immediately after World War II, when it had no effective rival. She does this through the lens of the magazine that, in the absence of any formal governing body, was effectively this strand of Protestantism’s voice and conscience: the Christian Century.