Short answers, pulled from the story.
The Ethnographic Atlas Codebook recorded that 588 out of 1,231 societies frequently practiced polygyny while only 186 were strictly monogamous. This data indicates that having multiple spouses was the historical norm for most of human existence rather than the exception.
Anthropologist Jack Goody discovered that polygyny in sub-Saharan Africa is a calculated economic strategy driven by the demands of agriculture and labor. Men seek multiple wives to monopolize their labor and childbearing capacity, or to generate male offspring whose labor is valued in regions where men perform more farming.
The Mosuo tribe of China allows women to remain in their maternal home and live with their brothers while property is passed matrilineally. This creates a society where the concept of paternity is secondary to the maternal line and women maintain significant economic independence.
Martin Luther granted a dispensation to the Landgrave Philip of Hesse to take a second wife in 1539. This double marriage was done in secret to avoid public scandal during the Protestant Reformation.
The landmark 1878 Supreme Court decision in Reynolds v. United States declared that polygamy was not protected by the Constitution. This ruling followed the Morrill Anti-Bigamy Act of 1862 which made polygamy illegal in all US territories.
Many Muslim-majority countries including Saudi Arabia, United Arab Emirates, and Qatar have not signed the covenant. In countries like Kuwait, no restrictions are imposed on the practice of polygamy.