What landed in my comments boxes (Was Hitler a Catholic?)

[Vetus Ordo]

Perhaps the  question should be, "Why were the Nazi party not formally excommunicated" ? Still an interesting question...

What kind of question is that? You can't "excomunicate" political organizations, only denounce and condemn them when it's due.

As for National-Socialism in Germany, check Pius XI's "Mit Brennender Sorge," on the Church and the German Reich.