“Once men turned their thinking over to machines in the hope that this would set them free. But that only permitted other men with machines to enslave them.” -Dune
I think it's logical to assume that the Jihad was against these slavers, destroying their machines, and the subsequent creation and enforcement of a prohibition against thinking machines, so that future similar enslavement wouldn't happen.
His son's books are terrible, they're steaming piles of shit. He's just milking his father's legacy for every penny he can get. Maybe there's some good books in that pile of shit? Not the ones I've read; I had to stop reading them when they created the Baron Vladimir Harkonnen golah and turned him into a retarded cartoon, completely betraying his, IMO, complex character in the original Dune. Read the first four books of the series and forget anything else exists. It ends with God Emperor Of Dune, there is nothing else.