A natural way of marriage is between one man and one woman.
Chapter 4 of the Quran allows a man to have four wives (4:3). This does not mean that every man should have four wives. This rule is an exception, and not to be taken in a general sense. The general rule is to have only one wife; but in a case of real necessity, a man can have more than one wife.
This need refers to a situation where, by some unfortunate incident, there is disparity between the number of men and women in society. When there are more women than men, there is sexual anarchy. To overcome this inequality, in dire cases, men are allowed to have more than one wife.
The truth is that a natural way of marriage is between one man and one woman. For a man is naturally biased against the second wife in most cases. This suffices to prove that monogamy is the natural way, while polygamy is permitted in exceptional circumstances by the law of necessity. There are exceptional laws of this kind which cover other cases as well. But exceptional laws are exceptional laws, and they cannot be applied in general.
Source: The Secret of a Successful Family Life