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. In this brief answer I will use the term “polygamy” with regards to a man marrying more than once, due to its widespread usage.
Polygamy is one of the main targets for criticism on the part of non-Muslims and even some who claim to be Muslims. However, polygamy is not something that appeared with the advent of Islam, rather it was present in human societies since the very beginning, and was practiced in many parts of the world.

The Context: Unrestricted Polygamy

Before the advent of Islam, polygamy had been practiced unlimitedly in many parts of the world. A man use to marry several women at one time. Even the Prophets (upon whom be peace) were not immune from it. Sayyiduna Ibrahim (peace be upon him) had two wives, Sayyiduna Ishaq and Sayyiduna Musa (peace be upon them both) had many wives, Sayyiduna Sulayman (peace be upon him) had several wives whilst Sayyiduna Dawud (peace be upon him) had hundred wives. In fact, there are only two prophets who never married, one being Sayyiduna Isa and the other Sayyiduna Yahya (peace be upon them both).
Historically, the Jews and Christians were polygamous. The ban on polygamy in Christianity is a man-made prohibition, not divine law. Polygamy was also practised among the Persians, Greeks, Arabs and Hindus. Unrestricted polygamy was permissible in all the religions before the advent of Islam.

Islamic Justice: Restricting Polygamy

When the Messenger of Allah (Allah bless him & give him peace) brought the message of Islam, polygamy was still a widespread and well-established custom. It was practiced without any restriction or limitation. Due to this, a man would marry many women, but failed to fulfil their rights, and the women who were in his marriage were oppressed and treated unjustly.
Islam came and banned the ill-treatment of women. It limited unrestricted polygamy that was the custom of the times of ignorance. It also laid certain conditions in order to practice polygamy.

Qualifying Conditions for Polygamy

The following verse of the Qur’an was revealed:
“If you fear that you shall not be able to deal justly with the orphans, marry women of your choice, two, three, or four, but if you fear that you shall not be able to deal justly (with them), then only one”(Surah al-Nisa, 3).
The circumstances in which this verse was revealed illustrate the sincere teachings of Islam regarding polygamy. It was revealed after the battle of Uhud, in which a significant number of Muslim men were martyred and as a consequence, many women were widowed and their children orphaned. To safeguard the new Muslim community, this just and compassionate law was revealed, and it remains in effect until the end of time.
Islam requires men to take full care of the orphan’s interests and property, but if they felt that they could not do justice to them as custodians, then they were advised to marry other women, up to a maximum of four.
Also, the Qur’an conditioned the permissibility of marrying more than one wife with justice and fair treatment. It is a grave sin to treat the wives unequally. Any man who wishes to take a second wife also has to meet the important condition of fair treatment of all his wives. The verse quoted above includes the command to treat wives equally, and anyone who is unable to do so should marry only one wife.
Equal treatment includes all social, economical and physical needs. It is very difficult for human beings to be completely fair, a fact which is recognised by the Qur’an:
“You are never able to be fair and just as between women, even if it is your ardent desire: but turn not away (from a woman) altogether, so as to leave her (as it were) hanging (in the air)… (Surah al-Nisa, 129).
The Messenger of Allah (Allah bless him & give him peace) said:
“A man who marries more than one woman and then does not deal justly with them will be resurrected with half his faculties paralysed.”  (Sahih al-Bukhari).
However, this refers to aspects that are within the capacity of a man such as equal treatment with regards to social, economical and physical needs. As far as the inclination of the heart is concerned, then that is beyond the capacity of a man.

Wisdoms Behind Polygamy

There is much wisdom why men have been given the permission to polygamy. I would just like to mention a few:
1) It is a known fact that there are more women than men and that they have a longer life. More men die due to wars and other incidents. The average life span of females is more than that of males, and at any given time one finds more widows in the world than widowers.
If we restricted men to having only one wife, then there would be many women without husbands. Especially, when a woman is divorced or she becomes a widow, at times it is very difficult for her to remarry. In permitting polygamy, there is a solution to this problem. These women will have someone to look after their social and economic needs.
2) At times, the wife is incapable of procreating and the husband desires to have children. Polygamy can also serve as a solution to this problem.
3) Some men are not satisfied with one woman. Recognising this need of a man, Islam permitted them to marry more than one wife, rather than falling into the trap of adultery and fornication.
In Western society, it is common for a man to have mistresses and/or multiple extra-marital affairs, in which case, the woman leads a disgraceful, unprotected life. The same society, however, cannot accept a man having more than one wife, in which women retain their honourable, dignified position in society and lead a protected life.
4) At times, the woman may not be able to fulfil the physical needs of her husband due to illness. By permitting polygamy, the door of extra-marital affairs is closed.
The above are just some of the reasons and wisdoms behind the permissibility of practicing polygamy. This is the decision of Allah, and we as Muslims must accept it.
Allah Most High says:
“It is not fitting for a believer, man or woman, when a matter has been decided by Allah and His Messenger, to have any option about their decision. If anyone disobeys Allah and His Messenger, he is indeed on a clearly wrong path.” (al-Ahzab, 36).
And Allah knows best
Muhammad ibn Adam al-Kawthari, UK