The reason we have monogamy as a standard, at least in the west, is mostly to do with it being the standard in Greece and Rome, not anything to do with Christianity. Though it probably would have caught on anyways, just for practicality's sake. You'll notice most places without the Greek and Roman influence still have monogamy. You'll notice that even societies where polygamy is a thing, it's a strict number. Polygyny is hot, but not really going to work as an actual institution, for the same reason monogamy was established in the first place, it causes too much individual competition between men, instead of fostering cooperation. At least in modern societies. As said, in times with higher death rates that disproportionately effect men, generally because of war, it makes a lot more sense. My understanding is that this was part of why it was so heavily practiced in Mormonism. It was part of the religion since its inception in the 1830s, but it became a more common practice following the civil war, at least from what I've been told.