Nationalism - in other words, the dividing of the church into bodies - consisting of such and such a nation, is a novelty, not above three centuries old, although many dear children of God are found dwelling in it.
When I go to Rome, I fast on Saturday, but in Milan I do not. Do you also follow the custom of whatever church you attend, if you do not want to give or receive scandal.
It took me fifty years to deal with the Holocaust at all. And I did it in a literary way.