Gedolim have written that part of the reason that a “Yom HaShoah” is against the Torah is that doing so mistakenly makes the Holocaust distinct from the rest of the bitterness of galus.
Just prior to the Holocaust, in Ikvisa DiMishicha, Rav Elchonon Wasserman made (in my humble opinion) a very insightful point. The two most common idols that some Jews worshipped pre-WW II were Nationalism (i.e. Zionism) and Socialism. Thus, Hashem sent a hybrid of those two, Nationalism-Socialism, otherwise known as the Nazis, YM”Sh, as a messenger of chastisement.
Other gedolim have written that Hitler YM”Sh was a messenger of chastisement for supporting/insufficiently protesting Zionism.
This may not explain the full horrors of the Holocaust, Hashem Yishmor, but it is obviously still very significant.
Then, Zionists during WW II, frustrated the rescue efforts of Rabbi Weissmandl (see Min HaMeitzar) and committed other various forms of treachery against Jews that cost untold numbers of Jewish lives. Before WW II, the things the Zionists wrote about Jews rivaled much of what the Nazis wrote and could have been the source of some of those Nazi opinions. And during WW II, the slogan of Zionism was “Rak BiDam Tihye Lanu HaAretz”. Zionists admit to this, too, and these things can be found on pro-Zionist sites as well.
It would be wise to understand how odious is this “Rak BiDam…” before even beginning to study that painful period of galus.
May Hashem redeem us all with the coming of Moshiach BB”A.