Monogamy is most common in America. In fact, it’s the law. It’s also taught in the Bible that a man is to be husband of one wife (however, this is only in respect to overseers of a church, not the common layman as far as I know).
In Africa, there are tribes today that still accept men marrying multiple women.
Here’s a question: If a man has multiple wives (and most likely children from them all) before he becomes a Christian, is he to divorce all but one wife, or keep them, after he becomes a Christian?