Many men in the bible had more than one wife and God showed favor towards them. Where and when did the concept of one wife marriges come to be?
Apparently the concept of one husband/one wife is as old as mankind. In Genesis 2:24 it says, “Therefore shall a man leave his father and his mother, and shall cleave unto his wife; and they shall be one flesh.” The scripture says wife, in the singular, and not wives in the plural. Furthermore, it implies (but does not state directly) that if he has another wife, then he is part of two (or more) bodies (flesh). Most people in the Bible had only one recorded wife.
The question, then, should be how and when the concept of multiple marriages came about. I don’t know how or when. In some cases kings entered into multiple marriages for political reasons. If you marry a princess from another country, then that king is not likely to attack you. In other cases it may have been selfishness, or a desire to avoid adultery.
I find nothing in the Bible that insists that all people adhere to the one man-one wife concept. There are prohibitions against adultery, but if he is married to multiple wives he is not committing adultery when he is with any of them, just if he goes outside of marriage. You just do not find “One man, one woman, for life” in the Bible.
I do find that under certain circumstances God did limit some people to one wife/husband. Paul told the church not add a widow to the list of those receiving support from the church if she had been the wife of more than one husband. (1 Timothy 5:9) Elders and deacons must have one, and only one, wife (1 Timothy 3; Titus 1). So any man who hopes to have a special designation in the church should be married to only one wife. (The statement of this as a requirement implies that there were some Christians who had more than one wife.)
In most places now, a Christian is limited to one wife because that is the law. Since we are to follow the laws of the land, and since many countries have laws against polygamy, Christians are generally limited to one wife.