I’ve only read 2 novels and want to get in to this. What title(s) cover the machine war?

Note that there are no "thinking machines" in any of the original Dune novels by Frank Herbert. His son has worked with Brian Sanderson to create several prequels which detail the original Butlerian Jihad (the war against the machines), and a sequel series that is supposed to be based on Frank Herbert's notes, but seems to quite clearly veer off (and that one recontexualizes some mysterious characters in from the last two novels as machines).

The encyclopedia goes into it as well but that was blessed by FH and not written by him.