I appreciate your comment here and for reading.

The part of the Holocaust that was unique was the systematic killing of Jews by the Nazis and the indignance felt by many internationally despite the fact that it was evident that concentration and extermination camps were killing hundreds of thousands of Jews.

This is to say nothing of the Einsatzrguppen, killing squads, death marches, and random acts of killing of Jewish populations without the direct incentive of Nazi command (Jedwabne, Poland, for example).

In Stalin's Soviet Union, the collectivization arguably did not particularly favor a particular nationality over another. During the Holodomor, for example, as Ukrainians call it, 1/4 of Kazakh civilians died. Many Russians and Belarussians, and others, were also victims.

There were the Gulags of course and the killing of hundreds of thousands by command directly from Stalin, but it did not have the racial purity violent undertones that sought to eradicate an entire people group.

Imagine if Stalin was forcing every Ukrainian into gas chambers. Our focus would be similar, if not the same.

I am not versed in Zedong's policies so I cannot directly comment there.

Hopefully, that's a sufficient explanation.