Earlier quoted context omitted.
In other places of the world polygamy was standardised. And wide spread religiously backed monogamy stabilisation didn't save us from two world wars.
The stabilising effect of monogamy isn't to prevent wars between nations and societies, it's to manage violence and conflict within a society. It works too and is not just a small effect. Of the 20 most unstable countries in the world, all 20 are very to somewhat polygamous[0]. [0] https://medium.economist.com/big-love-and-big-war-exploring-...
Just look what long celibate does to priests. Soldiers in war have to be 'neutralized' via some mild suppressants in the rations (at least WW II was done like this from what I had read).