“Satmar Rebbe said in his Hakdama to Vayoel Moshe that the sin of Zionism caused the Holocaust.
The Chazon Ish, R’ Henkin said it was because the Jews were violating the Oaths, which one of them was “that Klall Yisroel would not take control of Eretz Yisroel during golus”.
R’ Elchonon Wasserman Hy”d said it right in ther beginning of the tzoros. See his Ikvesa Dimshicha.
R’ Miller tells how he witnessed massive chilul Shabbos in Kovna.