The cause of the fall of multiple marriage in the West may with certainty be ascribed to its culture whose roots are not biblical but pagan Greek. The Hebraic culture and its biblical tradition of plural marriage first came to be seriously eroded when Alexander the Great appeared on the Middle Eastern scene. The activities of Alexander and his successors led to the rise of the infamous antichrist Antiochus Epiphanes whom Jews remember at Hanukkah each year. They began to increasingly impose Hellenic (Greek) culture on the nations they conquered. This clash between Yahweh's Torah (Law) and Greek humanism led to an attempt to exterminate the Jewish people and their laws altogether. Only a Jewish Maccabean revolt prevented this diabolical plan of Satan from succeeding.
This same Hellenic culture swiftly blended with the emergent Christianity in the first and subsequent centuries and created, first, a watered-down, and then a false Gospel called Catholicism which attempted to entirely erase Christianity's Hebraic roots. Biblical marriage was supplanted by the West's monogamy-only mindset with its attendant prostitution and homosexuality. The horrid decline in morality in the West may in large part be ascribed to the unnatural monogamy-only restriction.
The reason plural marriage is so vehemently opposed by so many Christians is not, I suspect, so much because they reject it as biblical (the honest can see it is plainly so) but because it represents a clash of cultures. Whatever the West is, it is not Hebraic - it is Greek. And the reason the Christian Church is dying in the West is because it is stubbornly clinging on to its Greek cultural roots, the very same culture which has always persecuted Yahweh's people and which has always been opposed to His Torah (Law). If the Church is going to survive and not be engulfed by the neo-paganism of the West, it must renounce its Greek legacy and return to its Hebraic roots.
The 21st century's polygyny-accepting churches and assemblies, with few exceptions, may be what are called 'Messianic' or 'Hebraic-roots'. Once you accept all of Yahweh's Law you are inevitably forced to accept biblical marriage, including a plurality of wives.
What was once natural for men and women, however, has - in the course of nearly two thousand years - become repulsive to your average Westerner. Ironically, this same Westerner is not indisposed towards sexual promiscuity and has eagerly embraced witchcraft and its sexual doctrine of 'help yourself without responsibility'.
In our view, the Western Church and its modern depraved neo-pagan culture has lost all authority. It is promoting a doctrine of demons. Believers in Africa and Asia particularly should not feel intimidated by them when the Western nations, and the United Nations which they control, condemn multiple marriage and use governments and agencies like the United Nations to try and enforce a monogamy-only culture that not only turns a blind eye to, but also promotes, promiscuous living.
For the last 30 years an end-time apostolic, Bible-based, Hebraic-roots community of Christians has been forming which, amongst other things, has declared the validity of plural marriage. It is known by various names, one of which is the Chavurat Bekorot, which in Hebrew means "Community of the Firstborn" (Heb.12:23). It has no connection with any of the historical churches or messianic groups but stands for itself as a fresh restoration of the biblical way of life. It provides the leaders for the congregations organised under its auspices..