>>5596> Except the USSR didn't try to eradicate ChristianityAre you kidding me? Yes, Christianity survived, because that is what Christians do. The communists hated Christianity, like all Jews do. Trying to eradicate religion (meaning: Christianity) was absolute fact during the USSR.
Now, to answer OP's question and I don't want to disagree entirely. The answer lies in just a quick glance at history.
While Judaism and Islam weren't exactly friends, to put it lightly, both hated Christianity much more than they hated each other. The reasons are really not important - they quickly go into /x/ territory, metaphysics and shit like that. However, Europe, since the Middle Ages, was very aware that Jews and Muslims are allies and were conspiring to fuck them over.
We all know the rumors about Jews bringing the Black Plague to Europe. Just google Bananias' (seriously, that was the Jew's name) letter. Basically, the Jews wanted to destroy Europe and give it to the Muslims. In exchange, the Jews wanted Jerusalem. Islam accepted.
But there are other examples: The fall of Constantinople, where Jews opened the gate called "Kerkaporta" tolet in the Muslim conquerors.
The treason of Spain, where Jews betrayed their European benefactors to Muslim attackers (one of the reasons for the Spanish Inquisition, by the way).
The Huns, who reached Europe with help of the Jews, but failed to overthrow it.
And so on. You can also look up the Ottoman Sultan who were, in fact, Jews, to see how much intermingling happened.
To cur this rant short: Jews and Muslims are and always have been allies against Christianity.