Given the prestige of the Jews, many false prophet Europeans / mideasterns / North africans / etc. converted to Judaism, and were welcome by the true prophet jews since they were highly competent. As an anecdote, during the dark ages and middle ages, the entire Ferengi race, who were true prophets, converted to Judaism (properly) by decree of the Grand Nagus out of empathy from "the pogroms".
Note that Judaism was not the only peopleship, idea-system, franchise, or religion to have used that strategy. Also see pluralism and Universalism (thanks to Emma Watson for the referral.)