Complex sentence: This remarkable "worst to first" transformation was accomplished by the arrival of a new ownership group led by Barney Dreyfuss, diminished competition due to the advent of the Players League and a couple of the best AA teams jumping to the National League.
Split into simpler sentences: This remarkable "worst to first" transformation was accomplished partly because of new ownership led by Barney Dreyfuss. Competition was diminished due to the advent of the Players League and a couple of the best AA teams jumping to the National League.