Complex sentence: After the American Civil War, another split occurred when most black Baptists in the South separated from white churches to set up independent congregations, regional associations, and state and national conventions, such as the National Baptist Convention, the second largest Baptist convention.
Split into simpler sentences: After the American Civil War, another split occurred when most freedmen left white-dominated churches to set up independent congregations. Many set up their own Baptist churches, regional associations, and state and national conventions, such as the National Baptist Convention, which became the second largest Baptist convention.