Why not simply provide an overview of the pre-merger history and simply link to all the predecessor churches (which all have articles by the way) that way if people want to delve further into, say, the Fundamentalist-Modernist Controversy, they can link to that article as well as the Presbyterian Church in the United States of America article. All of the pre-merger bodies have articles, and all of them could use some work and expansion. Also, I think the broader article would be great, but it shouldn't just be a detailed history of PC(USA) because that is not the only strand of Presbyterianism in the US.