Circumcision and Jewish Survival

Julius Wellhausen, "redactor" of the Document Hypothesis wrote on the closing page of his magnum opus Prolegomena to the History of Ancient Israel:

It is worthwhile to recall on this point the opinion of Spinoza, who was well able to form a competent judgment (Tract. theol. polit., c. 4, ad fin):--'That the Jews have maintained themeselves so long in spite of their dispersed and disorganized condition is not at all to be wondered at, when it is considered how they separated themeselves  from all other nations, but also by the sign of circumcision, which they maintain most religiously...' (page 548)

While not assigning exclusive credit for preserving the Jewish people Wellhausen/Spinoza emphasize that the peculiarity of the rite of circumcision provides an explanation for the survival of the Jews as a separate nation. This, is seems to me, is a eurocentric notion which fails to account the continued survival of Jews (a significant fraction of World Jewry at the time) for centuries under Muslim rule despite the fact that they too practiced circumcision  and many similar religious observances, and were generally much more hospitable (comparatively speaking at least).

But I find it more interesting that they found it necessary to ask the question in the first place.