People have become so degraded in this age that on the one hand they restrict polygamy and on the other hand they hunt for women in so many ways. Many business concerns publicly advertise that topless girls are available in this club or in that shop. Thus women have become instruments of sense enjoyment in modern society. The Vedas enjoin, however, that if a man has the propensity to enjoy more than one wife—as is sometimes the propensity for men in the higher social order, such as the brāhmaṇas, kṣatriyas and vaiśyas, and even sometimes the śūdras—he is allowed to marry more than one wife. Marriage means taking complete charge of a woman and living peacefully without debauchery. At the present moment, however, debauchery is unrestricted. Nonetheless, society makes a law that one should not marry more than one wife. This is typical of a demoniac society.
(Srimad Bhagavatam------4:26:6------purport).

Kāma-kaśmala-cetasaḥ also indicates that unrestricted sense enjoyment is not allowed in the human form of life by the laws of nature. If one enjoys his senses unrestrictedly, he leads a sinful life. The animals do not violate the laws of nature. For example, the sex impulse in animals is very strong during certain months of the year. The lion is very powerful. He is a flesh-eater and is very strong, but he enjoys sex only once in a year. Similarly, according to religious injunctions a man is restricted to enjoy sex only once in a month, after the menstrual period of the wife, and if the wife is pregnant, he is not allowed sex life at all. That is the law for human beings. A man is allowed to keep more than one wife because he cannot enjoy sex when the wife is pregnant. If he wants to enjoy sex at such a time, he may go to another wife who is not pregnant. These are laws mentioned in the Manu-saṁhitā and other scriptures.
(Srimad Bhagavatam------4:27:5------purport).

All the rules and regulations apply equally to the householder and the sannyāsī, the member of the renounced order of life. The gṛhastha, however, is given permission by the spiritual master to indulge in sex during the period favorable for procreation.
It is sometimes misunderstood that a gṛhastha, a householder, is permitted to indulge in sex at any time. This is a wrong conception of gṛhastha life. In spiritual life, whether one is a gṛhastha, vānaprastha, sannyāsī or brahmacārī, everyone is under the control of the spiritual master. For brahmacārīs and sannyāsīs there are strong restrictions on sexual indulgence. Similarly, there are strong restrictions for gṛhasthas. Gṛhasthas should indulge in sex life only in accordance with the order of the guru. Therefore it is mentioned here that one must follow the orders of the spiritual master (guru-vṛttir vikalpena). When the spiritual master orders, the gṛhastha may accept sex life. This is confirmed in Bhagavad-gītā (7.11). Dharmāviruddho bhūteṣu kāmo 'smi: indulgence in sex life without disobedience to the religious rules and regulations constitutes a religious principle. The gṛhastha is allowed to indulge in sex life during the period favorable for procreation and in accordance with the spiritual master's order. If the spiritual master's orders allow a gṛhastha to engage in sex life at a particular time, then the gṛhastha may do so; otherwise, if the spiritual master orders against it, the gṛhastha should abstain. The gṛhastha must obtain permission from the spiritual master to observe the ritualistic ceremony of garbhādhāna-saṁskāra. Then he may approach his wife to beget children, otherwise not. A brāhmaṇa generally remains a brahmacārī throughout his entire life, but although some brāhmaṇas become gṛhasthas and indulge in sex life, they do so under the complete control of the spiritual master. The kṣatriya is allowed to marry more than one wife, but this also must be in accordance with the instructions of the spiritual master. It is not that because one is a gṛhastha he may marry as many times as he likes and indulge in sex life as he likes. This is not spiritual life. In spiritual life, one must conduct one's whole life under the guidance of the guru. Only one who executes his spiritual life under the direction of the spiritual master can achieve the mercy of Kṛṣṇa. Yasya prasādād bhagavat-prasādaḥ **. If one desires to advance in spiritual life but he acts whimsically, not following the orders of the spiritual master, he has no shelter. Yasyāprasādān na gatiḥ kuto 'pi. Without the spiritual master's order, even the gṛhastha should not indulge in sex life.
(Srimad Bhagavatam------7:12:11------translation and purport).

In the Vedic culture there is a system known as satī or saha-maraṇa, in which a woman dies with her husband. According to this system, if the husband dies, the wife will voluntarily die by falling in the blazing funeral pyre of her husband. Here, in this verse, the feelings inherent in this culture are expressed by the wife of the brāhmaṇa. A woman without a husband is like a dead body. Therefore according to Vedic culture a girl must be married. This is the responsibility of her father. A girl may be given in charity, and a husband may have more than one wife, but a girl must be married. This is Vedic culture. A woman is supposed to be always dependent—in her childhood she is dependent on her father, in youth on her husband, and in old age on her elderly sons. According to Manu-saṁhitā, she is never independent. Independence for a woman means miserable life. In this age, so many girls are unmarried and falsely imagining themselves free, but their life is miserable. Here is an instance in which a woman felt that without her husband she was nothing but a dead body.
(Srimad Bhagavatam------9:9:32------purport).

Lord Rāmacandra took a vow to accept only one wife and have no connection with any other women. He was a saintly king, and everything in His character was good, untinged by qualities like anger. He taught good behavior for everyone, especially for householders, in terms of varṇāśrama-dharma. Thus He taught the general public by His personal activities.
Eka-patnī-vrata, accepting only one wife, was the glorious example set by Lord Rāmacandra. One should not accept more than one wife. In those days, of course, people did marry more than one wife. Even Lord Rāmacandra's father accepted more wives than one. But Lord Rāmacandra, as an ideal king, accepted only one wife, mother Sītā. When mother Sītā was kidnapped by Rāvaṇa and the Rākṣasas, Lord Rāmacandra, as the Supreme Personality of Godhead, could have married hundreds and thousands of Sītās, but to teach us how faithful He was to His wife, He fought with Rāvaṇa and finally killed him. The Lord punished Rāvaṇa and rescued His wife to instruct men to have only one wife. Lord Rāmacandra accepted only one wife and manifested sublime character, thus setting an example for householders. A householder should live according to the ideal of Lord Rāmacandra, who showed how to be a perfect person. Being a householder or living with a wife and children is never condemned, provided one lives according to the regulative principles of varṇāśrama-dharma. Those who live in accordance with these principles, whether as householders, brahmacārīs or vānaprasthas, are all equally important.

(Srimad Bhagavatam------9:10:54------translation and purport).

In India in those days and even until fifty years ago, polygamy was freely allowed. Any man, especially of the higher castes—the brāhmaṇas, the vaiśyas and particularly the kṣatriyas—could marry more than one wife. In the Mahābhārata, or the old history of India, we see that kṣatriya kings especially used to marry many wives. According to Vedic civilization there was no restriction against this, and even a man more than fifty years old could marry. But to be married to a man who had many wives was not a very pleasing situation because the husband's love would be divided among his many wives. To punish the girls unwilling to offer Him the naivedya, Lord Śrī Caitanya Mahāprabhu apparently wanted to curse them to be married to men who had at least four wives.
The social structure allowing a man to marry more than one wife can be supported in this way. Generally in every society the female population is greater in number than the male population. Therefore if it is a principle in the society that all girls should be married, unless polygamy is allowed it will not be possible. If all the girls are not married there is a good chance of adultery, and a society in which adultery is allowed cannot be very peaceful or pure. In our Kṛṣṇa consciousness society we have restricted illicit sex. The practical difficulty is to find a husband for each and every girl. We are therefore in favor of polygamy, provided, of course, that the husband is able to maintain more than one wife.
(Sri Caitanya Caritamrta------1:14:58------purport).

Every person must get married. Every woman especially must get married. If the women outnumber the men, some men can accept more than one wife. In that way there will be no prostitution in society. If men can marry more than one wife, illicit sex life will be stopped.
(Sri Caitanya Caritamrta------2:7:128------purport).