Polygamy means a system of marriage whereby one person has more than one spouse. Polygamy can be of two types. One is polygyny where a man marries more than one woman, and the other is polyandry, where a woman marries more than one man. In Islam, limited polygyny is permitted; whereas polyandry is completely prohibited.
Now coming to the original question, why is a man allowed to have more than one wife?
2. The Qur'an is the only religious scripture in the world that says,"marry only one".
The Qur'an is the only religious book, on the face of this earth, that contains the phrase `marry only one'. There is no other religious book that instructs men to have only one wife. In none of the other religious scriptures, whether it be the Vedas, the Ramayan, the Mahabharat, the Geeta, the Talmud or the Bible does one find a restriction on the number of wives. According to these scriptures one can marry as many as one wishes. It was only later, that the Hindu priests and the Christian Church restricted the number of wives to one.
Many Hindu religious personalities, according to their scriptures, had multiple wives. King Dashrat, the father of Rama, had more than one wife. Krishna had several wives.
In earlier times, Christian men were permitted as many wives as they wished, since the Bible puts no restriction on the number of wives. It was only a few centuries ago that the Church restricted the number of wives to one.
Polygyny is permitted in Judaism. According to Talmudic law, Abraham had three wives, and Solomon had hundreds of wives. The practice of polygyny continued till Rabbi Gershom ben Yehudah (960 C.E to 1030 C.E) issued an edict against it. The Jewish Sephardic communities living in Muslim countries continued the practice till as late as 1950, until an Act of the Chief Rabbinate of Israel extended the ban on marrying more than one wife.
3. Hindus are more polygynous than Muslims
The report of the `Committee of The Status of Woman in Islam', published in 1975 mentions on page numbers 66 and 67 that the percentage of polygamous marriages between the years 1951 and 1961 was 5.06% among the Hindus and only 4.31% among the Muslims.
According to Indian law only Muslim men are permitted to have more than one wife. It is illegal for any non-Muslim in India to have more than one wife. Despite it being illegal, Hindus have more multiple wives as compared to Muslims. Earlier, there was no restriction even on Hindu men with respect to the number of wives allowed. It was only in 1954, when the Hindu Marriage Act was passed that it became illegal for a Hindu to have more than one wife. At present it is the Indian Law that restricts a Hindu man from having more than one wife and not the Hindu scriptures.
Let us now analyse why Islam allows a man to have more than one wife.
4. Qur'an permits limited polygyny
As I mentioned earlier, Qur'an is the only religious book on the face of the earth that says `marry only one'. The context of this phrase is the following verse from Surah Nisa of the Glorious Qur'an:
"Marry women of your choice, two, or three, or four; but if ye fear that ye shall not be able to deal justly (with them), then only one."
Before the Qur'an was revealed, there was no upper limit for polygyny and many men had scores of wives, some even hundreds. Islam put an upper limit of four wives. Islam gives a man permission to marry two, three or four women, only on the condition that he deals justly with them.
In the same chapter i.e. Surah Nisa verse 129 says:
"Ye are never able to be fair and just as between women...." [Al-Qur'an 4:129]
Therefore polygyny is not a rule but an exception. Many people are under the misconception that it is compulsory for a Muslim man to have more than one wife.
Broadly, Islam has five categories of Do's and Don'ts: