Regardless of what century, nation or culture -— and assuming that sex selection abortion is not being practiced-— the natural ratio of male to female births is 1.05, meaning slightly more males than females are born. Thereafter the ratio typically flips because of males having *slightly* higher infant and childhood mortality rates. However there are still roughly equal numbers of males and females through young adulthood.
That means that, while it is possible for a few men to have multiple wives, it is NOT possible for *most* men to have multiple wives. If the top 10% of men (in terms of money, power or prestige) have four wives apiece, it necessarily means that the bottom 40% of men will have *NO* chance of ever marrying and establishing a family.
This creates extreme social instability, in that having large numbers of young men with zero marital prospects and zero investment in the future, means that you have mobs of unattached males becoming detached from any sense of social responsibility. You get criminal gangs or passive dropouts: predators or parasites.
Obviously that is not God’s glorious plan for Israel, let alone the whole human race.
If all have a right to seek a suitable marital partner, and most men form stable marriages and families as a societal norm, that means one husband, one wife, that’s it. That is what God wants for our well-being; there is no other way.
However, as political units grow larger, warfare increasingly occurs on borders far distant from most people's lives. Warfare also increasingly becomes the preserve of a specialized (or regionalized) military caste; the division of labor tends to separate the typical peasant from the need to bear arms except when things go very badly wrong on the frontiers (or Vikings start rowing up the rivers …).
Polygamy makes sense when boys start tending flocks at age 10 and become targets of constant raising from the clan from over the hill. When a very high percentage of young men die by violence at a young age, a tribal society will adopt polygamy to provide partners for the surplus young women. That's where the institution comes from.