There is no christian foundation in the New Testament against plural marriage.
Polygamy existed in the Christian world. It is documented that monogamy was adopted by leaders of the church in Roman times. Monogamy was a Roman practice and it was adopted by Christian leaders of the time in order to RECRUIT new followers from the Roman faith to Christianity. In effect, it was a compromise made to entice Romans to join Christian faith and it was made with no religious foundation what so ever!
Marketing caused the adoption of Monogamy in the Christian faith, not God.