Every single time polygamy was practised by people in the OT it always caused conflict and that was the cause of the downfall of Solomon, since he was dragged away from God by his multiple wives who kept their foreign customs. It caused conflict in the household of Abraham and the conflict got so bad that it forced the expulsion of Hagar. They were following the custom of the peoples around them and not what God wanted for them. Thy wee disobedient to God's clear command in Genesis f marriage simply being a union between one man and one woman, but according to the customs of the time that to show your power you had multiple wives and concubines. So by the results of their sinful actions we see the result of disobeying God's command for marriage. Since we have changed God's purpose for marriage and sex we are seeing the consequences of such actions in modern society.