Sheppard Si Sheppard 
Partisan Press [PDF ebook] 
A History of Media Bias in the United States

This book is the first to place the contemporary debate over media bias in historical context, illustrating how partisan bias in the American media has built political parties, set the stage for several wars, and even contributed to the rise and fall of U.S. presidents. The author discusses the rise of the unprecedented post-World War II model of objective journalism and explains why this model is breaking down under the challenge of a new generation of technology-driven partisan media alternatives.