I have a friend who consistently relates any conversation back to their set topics. Such as North Korea, nazis,soviet union, freemasons and greece. For example, I was talking about disney killing off big characters in their franchises they have bought. And he replies
"oh,hes doing a stalin"
And then lists times when stalin has killed some people for some reason or another. Most times it's like 10% related to what we are talking about, but if we go back onto the original conversation, he will find another way to relate back to one of his chosen topics.
It's quite annoying and I want to know what it's called so I can talk to him about stopping it. If we entertain it he wont stop!
Someone suggested "circular conversations"