In response to this post in which I begin to offer some hypotheses on the causes of decline of the mainline, Martian Mariner posted

Are you saying that the decline of the mainline denominations started at the time of the abolitionist movement, or just that a path of thinking had been started which would eventually lead to the decline?
Also, the issue of slavery obviously split the American Church as it split the nation. How was this split viewed by congregants at the time, and how has that continued cultural difference between Northern and Southern churches (PCUSA/PCA; AmBaptist/SBC; etc..) affected the views of congregants in more modern times?

The decline of the mainline denominations did not start at the time of the abolitionists. My point was that a "path of thinking" did indeed start which had as one of its indirect outcomes mainline decline. When the story of the growth of liberalism in American denomination is told, I think the story of abolitionists is overlooked, but very important.

Regarding regionalism in American Christianity. Southern Christianity during the antebellum period viewed itself as the preserver of biblical Christianity in the face of the heretical abolitionists. In my research in religious periodicals of the period I have found Lincoln often referred to as "that godless Lincoln." The southern churches locked into a literal reading of Scripture. Some of this attitude continues today.