FT's editor, Joseph Bottum, offers a provocative overview of America's Protestant history in The Death of Protestant America: A Political Theory of the Protestant Mainline.
As my blogbrother Jonathan Rowe has noted, it's quite difficult, especially for Christians themselves, to decide just what "Christianity" is. Bottum quotes historian Gordon Wood that by 1800,
“There were not just Presbyterians, but Old and New School Presbyterians, Cumberland Presbyterians, Springfield Presbyterians, Reformed Presbyterians, and Associated Presbyterians; not just Baptists, but General Baptists, Regular Baptists, Free Will Baptists, Separate Baptists, Dutch River Baptists, Permanent Baptists, and Two-Seed-in-the-Spirit Baptists.”
Oh, my. Like that Reynolds fellow says, read the whole thing.