If Hitler had gotten his way, the "Third Reich" would have stretched far beyond the traditional borders of Germany itself, swallowing up vast stretches of other European territories. For a time, it was exactly that. We follow the Germans into Austria, the Slavic nations, Poland, France, Belgium, the Netherlands, and Russia.
Even so, Shirer's focus is on Nazi Germany itself—the place where Hitler's attempted "Nazification" of Europe began, and the center point from which all of the Fuehrer's invasions, incursions, occupations, and assaults radiated outwards to the world beyond.
For more info on the setting, just…read the rest of the guide. The historical context is mixed in with every single piece of content, so you have everything you want at your fingertips.