The Old Testament where you find all those cases of polygamy was just a SHADOW of THE REALITY to come in the New Testament. People hold to SHADOWS, not real love. Real love joins you to each other for eternity
There is no such any bible verse that says a polygamy is legal. Polygamy is only legalize in some countries in the world because their gvornment allows it, not by God. Polygamy is very popular to Muslims, but in my opinon, maybe they are doing that because Abraham did have two sons in two woman and it is because God says it to Abraham.
Although God says it to Abraham, there are no bible verse in the Old and New Testament that God says you must have two wives.
Polygamy is against the law of God.