"As is well known, Judaism permitted and even encouraged polygyny (“many wives”) for centuries until Rabbeinu Gershom (c. 960-1028) enacted an edict against marrying more than one wife, unless allowed on special grounds by at least 100 rabbis from three different countries. Interestingly, Rav Yaakov Emden explains, the reason for the ban was not moral or spiritual, but social. The edict was a reaction to the danger that having more than one wife could bring to the Jews in a Europe increasingly dominated by Christianity, which had been trying to abolish polygamy from about 600CE to 900CE. In short, the purpose of the edict was to protect the Jewish people from being attacked or even killed by resentful Christian fundamentalists. Furthermore, according to most authorities, the ban was supposed to have validity only until the end of the fifth millennium of the Jewish calendar, so it never actually had the force of an edict (cherem) after the year 1240CE, though it continued as a custom in many places. (Originally, the prohibition was also limited geographically to certain European countries and regions.) If the Torah and the biblical law permitted polyamory, if the rationale for the prohibition was contextual, and if the validity of the edict was supposed to last only until the year 1240CE, then the current observance of the Cherem Rabbeinu Gershom seems unjustified. Of course, in light of the modern reconstruction of Judaism carried out by Rabbi Michael Lerner and others (see Lerner’s The Jewish Renewal), contemporary Jews may regard the traditional endorsement of polygyny and prohibition of polyandry (“many husbands”) as a “sexist” trend of ancient Judaism and, consequently, may want to creatively explore more egalitarian forms of polyamory."