30,000 Uyghur women and children weren’t indiscriminately bombed to death via advanced drones, nor were hundreds of innocent civilians massacred at hospitals in China and buried in mass graves. It’s happening in Palestine as we type.
And indeed, when the Nazi's were losing they tried quite hard to hide the evidence, however it was so total and immutable in many cases that it could not be hidden, mostly because the allied powers controlled their lands and had free access to their previously governed population..
Without such access proof rarely escapes and when it does the total brutality is considered impossible; this is exactly what happened during world war 2.