Monogamy was introduced to the Jewish people by the Romans. Romans were pagans at the time.
Romans were monogamous before Christianity.
Monogamy's spread in the West had something to do with the influence of Christianity, but not as much as you might expect. Mainstream Christianity has always endorsed and enforced monogamy, and as Christianity spread across Europe in the centuries following the fall of Rome, monogamy spread along with it. However, Christianity's condemnation of polygyny has never been as straightforward as anti-polygyny church leaders would have preferred, because no Biblical passages explicitly prohibit plural marriage.
The case for an automatic association between Christianity and monogamy is weakened further by the fact that socially imposed monogamy was first established in ancient Greece and Rome, centuries before Christianity even existed. Greco-Roman laws prohibited any man from having more than one official wife at a time.
https://www.psychologytoday.com/intl/blog/darwin-eternity/201109/why-we-think-monogamy-is-normal