Polygamy
Question
Why has modern Judaism out lawed Polygamy and yet many ancient sages didn't.
Answer
Shalom!
Thank you for your question.
Indeed, polygamy was originally permitted. However, the great sage, Rabbeinu Gershom banned the practice in about the year 1000 CE.
Rabbeinu Gershom made a number of enactments that are followed to this very day, but perhaps his ban on polygamy is the most famous one.
There are a number of interpretations and explanations for Rabbeinu Gershom’s ban. Among them: in order to better ensure peace between husband and wife, to better ensure that a husband can provide for his wife, to prevent strife in the home, and to ensure men would not marry women who they would not be able to support, among other explanations.
Although originally it was only an Ashkenazi enactment, the ban on polygamy has been universally accepted in the entire Jewish world.