The title really says it all, but if you're still reading, you want more detail.
So ever since I played my first historical wargame I've been reading history. A lot. So immediately after I finished reading A World Undone I launched myself into Rise & Fall of the Third Reich. After all, in the story of WW1, probably one of the most compelling character is Germany, and WW1 ends on such a cliff hanger.
To go with my history books, I like a good solo friendly history game. So I'm playing A Victory Denied and I'm reading Rise & Fall of the Third Reich. Suddenly something clicks. Because I'm reading about the concentration camps. I'm reading about all the horror of them. Probably the most vivid and repulsive part was describing the Nazis gassing people with interesting tattoos so they could make lampshades out of their skin.