Dan Carlin is great, but you should take his warning that he's not a historian to heart: he enthusiastically speculates and characterizes the people in a way a historian would not, and can be very guilty of picking and choosing events to support the narrative he paints. You will almost certainly get a better understanding of the topics from looking at the academic materials from which he bases his own podcasts.

That said, enjoy him—he really does make the topics come alive, and I haven't been satisfied with JUST his podcast after he's piqued my interest. That's a great thing.