> Begins?...
Yes it was normal in probably all cultures and societies and still is, officially, in a few, and unofficially in many.
There probably is a tendency for rich and powerful men to demand and acquire more women, but I think that's rarely the norm. If the top 5% of the men conrol 20% of the women, that means the bottom 20% of the male population, having no chance of marriage, comprise a eunuch or homosexual underclass. Not good.
I think this article (Link) on the history of marriage probably provides a more realistic view of how monogamy came to be seen as culturally optimum.