One of the surest patterns in Jewish history is that Jews who convert to Christianity become the worst enemies of the Jews.
Around 1240, a Parisian Jew named Nicholas Donin, who had converted to Christianity, convinced the king of France, Louis IX, that he would be able to prove the truth of Christianity through the Talmud. This is the same claim that Pablo Christiani, another converted Jew, would make in Spain in 1267 in his famous debate with Nachmanides.
The Church was always partial to converted Jews. Donin was very ambitious and had visions of rising high in the Church. Convincing the authorities that you could prove Christianity through the most authoritative book unique to the Jews was a sure path up the ladder to success in the Church for a Jewish convert. By winning such an argument, all the Jews would convert it was believed.
Louis ordered the rabbi of Paris, Rabbeinu Yechiel — mentioned many times in the Tosafos commentary of the Talmud — to debate Donin. All of the debates in Europe were losing propositions for the Jews. If they won they lost and if they lost they lost. There was no freedom of speech. Only Nachmanides succeeded in winning the right to free speech, and even after he won the debate he and his community faced intensified persecution for his efforts. In all other debates, one could say nothing that would be critical of the Church or Christianity, effectively making it not a debate at all.
Nevertheless, Rabbeinu Yechiel made such a skillful defense that the king agreed that it was true that one could not prove Christianity through the Talmud. Nevertheless, he said that the Talmud was an insult to the Christianity.
Therefore, in 1242, he ordered the burning of 24 cartloads of priceless Hebrew manuscripts. We have to bear in mind that in the Middle Ages each book to be hand-written. The Talmud alone is, in today’s format, about 2,300 pages. They wrote using quill pens and manufactured ink on parchment (or vellum paper that then began to be produced). The pure physical labor of sitting and writing that volume of words alone boggles the mind.
The 24 cartloads amounted to some 12,000 volumes. Louis had all the copies of the Talmud he could get his hand on collected and burned them. For his efforts, the Church canonized him as a saint in 1297. (He is the famous Louis after which the American city and baseball Cardinals are called after.)
That event effectively marked the end of the Jewish community in France. The king followed it up with an expulsion of the Jews from France — after despoiling them, and taking away their money and property, of course. The Jewish community in France never really recovered. It never again became the great seat of learning or even the great seat of Jewish tradition as it was in the 11th through 13th centuries.
Today, the majority of Jews in France are Sephardic Jews who came from Algeria, Tunisia and Morocco within the last century. It is not a scholarly or a particularly strong Jewish community. It certainly never again looked like Rashi’s community, after they burned the Talmud.