In this nice short video, Sheikh Yusuf Estes talks about the fact that it is allowable for a man to have more than one wife up to four wives while a woman is only allowed to have just one wife. Enjoy watching this video to know why Islam allowed this and prevented the other.
Sheikh Yusuf relates a story of a woman who came to ask him this question and how he answered here. He adds that in spite that having four wives is allowed in Islam, you may find 1 percent or two percent who has it because it, as some might think, is not related to sexual purposes. Rather, it is a kind of additional responsibility which the husband bears.