manipulation in mass media
Historically, TV channels and newspapers were the primary sources of news... and because their owners were ultra-rich, the news that reached the general public was communicated in such a way to promote the interests of the ultra-rich, using various tried-and-tested strategies.
What we have now with the rise of the web, and particularly with social media, is the democratisation of news, in that
in theory anyone can be a source of news, and there is no filtering through a biased gatekeeper. But this has some unfortunate consequences, too. One is a lack of accountability, so that things may be presented as factual even with no supporting evidence (or, often, in complete opposition to available evidence). Another is that nothing that is important remains truly democratic for long... the rich and powerful now use social media to promote their own agendas, as they already do with TV and newspapers. And they can now be more insidious in their approach.
The basic issue I think can be distilled into two points:
1) The rich and powerful will always try to influence what is available to the public, and try to present it in such a way as to direct public opinion, and
2) Any mechanism of communication that starts off free and democratic will, if it becomes sufficiently important, fall under the control of the rich and powerful.