I didn't say that monogamous society is unsuccessful. I merely said that we are not perfectly monogamous -- we cheat, we have one night stands, we have threesomes. If those activities weren't successful reproductively, natural selection would have ensured that we don't do them.

In fact, there are arguments that monogamy was put in place by lesser-status males to ensure that they have access to women; without societal encouragement of monogamy, women tend to flock to very high status men -- "alpha males," though I think that term is reductive -- leaving lower-status men alone. You can see this with the groupie phenomenon -- as soon as a male achieves a high level of fame or riches, wouldn't you agree that he has access to a much higher number of women? But if a rock star is married, it leaves more women for the "rest of us."

I'm not saying that's an indisputable fact. That's just the theory.

As for Western Christian society's domination, you might want to check out Guns, Germs, and Steel (man, I'm a regular book club over here) for an excellent explanation of why this came to be. In a nutshell, the author argues that the initial environment of the birthplace of Western society, the Fertile Crescent, was much richer in food and livestock resources than anywhere else, and that this advantage gave the Western world a huge head start. Successful agriculture led to food surpluses which led to thinkers and inventors having time to think and invent rather than being forced to grow their own food, which led to superior technology and strategies for using it. With these superior elements (with a lot of help from epidemic diseases that developed as a result of having close-packed city populations and to which most native societies had no immunity) they went on to conquer the world. In the book, monogamy doesn't figure into it too heavily, but I agree that it probably played a part.