Their part in his downfall
In the sense that World War II is currently a hugely popular draw in movies and books, Diarmuid Jeffreys and Mark Mazower have timed their arrival in the market well.
Their books are very different. Jeffreys focuses on one relatively small aspect of the war, IG Farben and the chemical cartel which was deeply complicit in Nazi atrocities, particularly the Monowitz plant in Auschwitz, where children were routinely blinded, castrated or had organs removed in the name of research.