I am curious as to where it all comes from. Was there a specific catalyst for the conspiracy taking off?
Disclaimer - the holocaust happened. Not denying it. Just wondering when denial started.
User /u/commiespaceinvader replied to this post with what I think is about as definitive as you can get on the Internet: https://www.reddit.com/r/AskHistorians/comments/68uu11/how_prevalent_is_holocaust_denial_and_how_does_it/
Additionally the wiki has answers: https://www.reddit.com/r/AskHistorians/wiki/faq/militaryhistory/wwii/nazigermany#wiki_holocaust_denial
Of course further answers are possible