Complex sentence: James found that the contemporary baseball guides did not consider the Union Association to be a major league either: the earliest record he could find of the Union Association as a major league was Ernest Lanigan's "The Baseball Cyclopedia", published in 1922.
Split into simpler sentences: James found that the contemporary baseball guides did not consider the Union Association to be a major league either. The earliest record he could find of the Union Association as a major league was Ernest Lanigan's "The Baseball Cyclopedia", published in 1922.