WHEN Hitler’s forces marched into Warsaw in September 1939, Wladyslaw Bartoszewski’s parents told him not to panic. They had experienced German occupation during the last war. There would be inconvenience, disorder and even looting. He should be careful. But it would not be too bad—the Germans were, after all, west Europeans—and by next year, the British and French would arrive. The Bartoszewskis could hardly have given their teenage son worse advice. The Western allies never came; instead the Soviets joined in the Nazi attack. Hitler not only wiped Poland off the map, but aimed to obliterate its language, culture and...