That a mosque was allowed to be built in the first place was the beginning of France's downfall.
_______
You don't think maybe the Germans might have had a little to do with it?
The mosque was founded in 1926 as a token of gratitude, after World War I, to the Muslim tirailleurs from France's colonial empire, of whom some 100,000 died fighting against Germany.
...
During World War II (when France and Paris were occupied by Nazi Germany), the rector Si Kaddour Benghabrit managed the mosque to serve as a secret refuge for Algerian and European Jews. He ensured they were provided shelter, safe passage, and fake Muslim birth certificates to protect them from German persecution. Wikipedia