Of course, nobody could even imagine the absolute horror of the Holocaust.
The Armenians could. As could the Nambians. As could the residents of Nanjing, China and Gando, Korea.
But these mass murders were so chronically under-reported - even deliberately suppressed - in media controlled by the political opposition and its allies, that it was possible to never know they'd happened much less consider they could happen locally.
I would also note how the Israel assassination of journalists across Gaza and the West Bank has gone a long way towards suppressing the size and scale of their genocide, particularly at the upper reaches of western media. You absolutely can talk to people in DC or London or Berlin who will (either deliberately or out of their own cloistered media consumption habits) not recognize the scale of atrocity.
But even if you could have convinced someone staring into a cattle car in Poland or Austria that this was the beginning of the end, what would you expect this person to do? Surrounded by armed men who were, in turn, surrounded by tanks and supported by bombers, how were they expected to respond?
The countries had already been defeated. Their people had already been broken on the wheel of war. They were civilians without the training, much less the materials, to mount any kind of guerrilla campaign. They had no Che Guevara or Ho Chi Mein or even a Huey P. Newton to rally them. There certainly wasn't a Mao on hand to lead them in a Long March for their survival and eventual return.
They'd put their trust in the established state lords. Those lords had failed. And now there was nothing standing between them and the gas chambers. Feels trite to say they all should have rushed the guards in a mob, when the Charge of the Light Brigade was the last famous incident of such epic folly.
