Let’s take the Lakota and Comanche native American nations as examples. Aside from just being inherently fascinating, they’re interesting examples because polygamy became exacerbated in these societies due to outside economic forces.
He cites Lakota America: A New History of Indigenous Power by Pekka Hämäläinen:
A skilled tanner could finish twenty-five to thirty-five robes in a year — which fetched three to six guns — whereas a skilled hunter could bring down ten bison in a single chase. This made women’s labor the most critical resource of the robe trade, which, in effect, was a mechanism for connecting western female labor and expertise to eastern demand for furs. Women’s labor was the bottleneck in Lakotas’ quest for goods and wealth, and like many other Indigenous societies enmeshed in colonial markets, they widened that bottleneck through polygamy. The practice was ancient among the Lakotas, but it grew dramatically with the robe trade.
He continues:
Women’s roles in buffalo robe production meant they became the economic bottleneck with the buffalo robe boom, raising the value of wives as instruments of production. This led to a cycle of rising inequality: wealthier men could afford more wives, who could then generate more wealth and accumulate more wives.
[…]
The accumulation of wives by elite men led to a bride deficit. There were fewer brides to go around for under-performing males. This heightened intra-male competition.
[…]
Without monogamy, successful men hoard wives and sire more children and there are more men with neither wives nor children. A society with fewer disaffected men is more stable. Such disaffected men benefit from volatility: they’re willing to take bold bets to win status and wives. Crime, revolutions. They have everything to gain and nothing to lose.