They avowed that that Berlin was their Jerusalem. They disavowed any connection to the Land of Israel. The Jews have to be. All other nations rise and fall and vanish. But from the moment that G-d made Israel the instruments of His Will, their existence is as immutable as His existence.
Assimilation is like a nuclear chain reaction.
When a certain critical mass is reached, then the atom bomb of anti-Semitism explodes. No nation represented the summit of culture and refinement more than pre-war Germany, and yet within a few short years it turned into a savage beast. Holiness can only exist when it is separated from that which is not holy. If everything is holy, nothing is holy. When the Jewish People forget that their purpose is to be a holy nation, separated from the other nations, then the non-Jewish world turns around and remind us of our purpose.