There are many aspects of this, and what can be presently proven is always an extremely small tip of the iceberg. I've read a lot of different historical accounts and it is practically a given that all these mechanisms or even institutions and practices which existed up to recently aren't magically dismantled in the present moment. For the start, read about the practice of "embedding" journalists or about:
https://foreignpolicy.com/2013/07/14/u-s-repeals-propaganda-...
Then consider (if you are old enough) about what the public perception of such coverage was, at the given point of time. Basically, with enough distance in time, we can easily read about the huge distortions, and just shrug and say "yes it was so" but somehow too many people assume that the present moment is somehow, by some magic, "clean."
My favorite example is the
https://en.wikipedia.org/wiki/Iraq_Dossier
"a 2003 briefing document for the British prime minister Tony Blair's Labour Party government. It was issued to journalists on 3 February 2003 by Alastair Campbell, Blair's Director of Communications and Strategy, and concerned Iraq and weapons of mass destruction."
An apparent "proof" turned out to be "plagiarised from various unattributed sources including a 13-year-old thesis produced by a student at California State University."
If something that obvious (after the fact) was used as a proof for many nations to go to war, and readily repeated by all the media, what do you expect from the rest of the coverage? I personally remember the coverage from that times, it was considered "patriotic" to not even try to point to the better verified facts.
Being surprised about the fact that the direct agendas are behind most of the "news" production is just like being surprised that "there are exactly that much important news in the world per day to fit the front page of the newspaper."
Regarding "embedding" I remember reading different articles about the journalists and editors being directly enlisted by some agencies to "independently" provide "patriotic" coverage, even while operating in the mainland, not in some foreign war zones. Maybe somebody saved some such link, I haven't, and Google is not helping me.
The current state is not different, to paraphrase James Mickens, even now these players could without problem claim "we are not doing this" while at the same time wearing the t-shirts "we are totally doing this" and... only the first part will be in the titles.