From the text of scripture and from the historical records of the time we can conclude that polygamy was not known among the Jews or the Romans during the time of Christ. Yet, in His answer to the Pharisees about the Mosaic permission concerning divorce, we can see that polygamy also fits into this category of something permitted for a time but never part of God's original plan. Here is part of the discussion between Christ and the Pharisees on this subject.
Mark 10:4 And they said, Moses suffered to write a bill of divorcement, and to put her away.
5 And Jesus answered and said unto them, For the hardness of your heart he wrote you this precept.
6 But from the beginning of the creation God made them male and female.
7 For this cause shall a man leave his father and mother, and cleave to his wife;
8 And they twain shall be one flesh: so then they are no more twain, but one flesh.
9 What therefore God hath joined together, let not man put asunder.
Notice a couple of facts. From the beginning of the creation, God made humans as male and female so that a man could leave his parents, cleave unto his wife, and the two should be one flesh. If this teaching (taken from Genesis 2:21-24) restricts divorce, it even more strongly supports monogamy in marriage. God never set up for three to be one flesh. The Old Testament permission was just that--permission based on the hardness of their hearts. The divine plan is for one man and one woman to join in marriage and become one flesh.
Paul also refutes polygamy by his teaching. 1 Corinthians 7:2 states, "Nevertheless, to avoid fornication, let every man have his own wife, and let every woman have her own husband." Certainly, this statement makes no sense apart from marriage being a monogamous joining. Paul makes no provision for polygamy. Neither should we.