My (non-authoritative) understanding was that after Vietnam there was a more recognised need to control what the media published, resulting in Operation Mockingbird and such. However, given how centralised the media has always been, I could see it being influenced before this.

Did you have any examples or reading to share?

I really shouldn't be so gobsmacked by people's ignorance of history, but it is astounding to me the number of replies here that seem to believe that the press really was well-behaved in this time period. When learning about the Spanish-American War, pretty much the most important bullet point covered in history class is the role of the press in essentially inventing the cause of the war, as exemplified by the infamous quote from a newspaper baron: "You furnish the pictures and I'll furnish the war."

The general term to look up is "yellow journalism."