Title.

Most research suggests that for 99% of human history, human relationships were hypergamous and polygamous. With the concept of monogamy and "marriage" between 1 man and 1 woman popping up only a few thousand years ago in Mesopotamia:

https://theweek.com/articles/528746/origins-marriage

At some point during the rise of Roman Catholicism in Europe, and a subsequent rise in the human population, the concept of monogamy became very heavily enforced by the law. With some places in Europe having adultery laws punishable by death. And with divorce being strictly prohibited, or only allowed under extreme conditions. With some Germanic courts only allowing for "Divorce by Combat", where the husband and wife must fight to the death in a duel; taking the vow "till death do us apart" quite literally.

https://www.ancient-origins.net/history-ancient-traditions/divorce-combat-0017263

This is generally considered to be where monogamy as we know it entered the scene. But why? I can't find any historical evidence as to what exactly happened to prompt this change. If polyamorous relationships where 1 man with many women is the natural way humans reproduced for like 99% of our existence, why was monogamy so deliberately implemented?

Surely, there must have been some compelling reason or it never would have happened.