Basically, multiple wives was as normal as multiple children around the world since the beginning of time (not that everyone did it, of course, not everyone preferred to).

Then the pagan Greco-Roman culture developed a prejudice against it. Aristotle said that restricting people to one wife helped the government control them (which they saw as a good thing ?).
It became part of their cultural pride (the Greco-Roman culture is possibly the most arrogant pagan culture on earth). They saw others as barbarians: hairy, grunting, sweaty savages with harems and sexual passions that were disgusting to the posh, high-brow Greco-Romans. This was all centuries before Christ.

The fact is, Abraham, David, and Christ our Lord are among those "hairy, grunting savages" that they despised.

Constantine and others remade the faith of Abraham to look basically the same as Greco-Roman culture, and then forced people to follow their culture "in the name of God". You know how far the Roman Empire spread, and how far Roman Catholicism spreads even today.
Here's a quote: "If any one saith, that it is lawful for Christians to have several wives at the same time, and that this is not prohibited by any divine law; let him be anathema." - Council of Trent, 1545-1563

This is where the cultural prejudice against multiple wives in European culture comes from originally.

Then you have the Mormon cult, which at first did forced marriage and incest and other horrible things. America outlawed multiple wives in order to stop the Mormons from gaining power (the government used the cultural and "religious" prejudice to justify it, but it had nothing to do with following the Bible or any such thing).
Since then, most nations were trying to copy America in outlawing multiple wives.

Nowadays people even claim outlawing multiple wives is about women's rights, even though by definition women are more than two thirds of the people doing it. ?

Many Christians are doing things according to Greco-Roman tradition (like observing "Sunday" each week), and now that the governments are encouraging and even enforcing the old Roman prejudice, they try to twist Scripture in order to condemn multiple wives.