I have written about this elsewhere in the past. It is definitely worth repeating. Try looking for this mechanism in whatever context is most real to you. You should be able to find it.
The “third party” referred to here would normally be someone who’s pretty crazy. There are some examples in history of hate-mongers creating propaganda campaigns against whole groups to justify genocide. But this tactic can also be used to create violence or war between nations or individuals. Most of those activities, being more covert, are not as well reported in history or the social sciences.
Of course when the “third parties” are running the show you get wholesale denial that this mechanism even exists. But I suggest you look for it. Hubbard says it’s a law; maybe he’s right!