Polygamy for men shows shows how excellent the woman is when she can be fulfilled by one man. And how empty the man is because he needs more the one woman.
According to sacred law a Muslim man can marry a women who is a Christian or Jew and or sabeans (believers in the Prophet Yahya - there are some of these in Iraq).
A Muslim woman can only marry a Muslim man. Why? This seems like its wrong doesn't it? Please let me explain. A Muslim man has to respect the religion of his non-Muslim wife, he believes in her Prophet, Moses, Jesus and Yahya (upon them all peace).
He respects her book and he has to by sacred law to pay for her daily needs: food, housing etc. A non-Muslim man on other hand doesn't believe in her Prophet or religion. So he could cause her to loss in her religious action.
For example he might prevent her fasting because he doesn't like it or he might stop her praying. He may also refuse to pay for any of her daily needs, he not obliged to do this.So the reason here is, that the non-Muslim man cannot fulfill her rights either worldly or religiously. If he did then he would be Muslim. This is in order to protect the woman from harm.
Does this make sense, please ask me to clarify if you do not understand.