calendar - 20 Sivan and the inappropriateness of new days of commemoration

The kina (elegy) "Mi yiten roshi mayim" recited on 9 Av was composed in commemoration of the events of the First Crusade as it passed through the Rhineland. It includes the following lines (freely translated):

And because one ought not add a day to the calendar commemorating destruction...
I will instead arouse my cries of "woe!" today [i.e., 9 Av]

One could, one might think, dismiss this viewpoint as one that was not accepted as normative halacha/hashkafa. One could, except that there are those who applied this consideration, in practice, to the Holocaust, saying one should not add a day to the calendar (e.g., Yom Hashoa) commemorating it. (I see this argument attributed to Rabbi Joseph B. Soloveitchik.)

My question is, what do such opinion-holders do with 20 Sivan, which has a history of great rabbis' support, and commemorates post-churban tragedies?

Answer

R' Moshe Feinstein zt"l explains (Igros Moshe, vol. 8, Yoreh De'ah 57:11) that the statement in the kinah is referring to tragedies affecting all of the Jewish people. The Crusaders wanted a wholly Christian world, with no Jews ר"ל (and indeed, they attacked and killed the Jews in Jerusalem as well as in Europe); Hitler's ימ"ש aim was similar. Such calamities are a continuation of the Churban and are included in our mourning for it.

By contrast, he says, Chmielnicki's ימ"ש massacres were a local event, and were not government-sponsored (indeed, the Polish authorities, against whom the Cossacks were revolting, tried to save the Jews where possible). So while it is indeed an outgrowth of galus (in his words, "משום דמאותן החטאים שנתחייבנו בגלות נענשנו גם בזה", "because it is due to the same sins for which we incurred galus that we were punished with this too"), it is something different and deserves its own (local) commemoration.

(R' Moshe doesn't seem to deal with the fact that 20 Sivan had first been established as a fast day several centuries earlier, by Rabbeinu Tam, memorializing the Jews killed al kiddush Hashem following the Blois blood libel of 1171. Perhaps, though, the same logic applies: it occurred in one particular city, and was not sanctioned by the king of France, only by the local baron.)

(Source found in this post.)