Big problems with polygamy. Polygamy causes problems. Rich men get all the women. In their innermost minds, poorer men hate the religion that derived them of wife and children. They are forced to direct that hatred outward, toward the rich, monogamous cultures around them.
Polygamists encourage young men to blow themselves up. Every young man who destroys himself lessens competition for wives, lessens the chances for revolution, and weakens their opposition.
Polygamous societies produce so many angry young men that they can only survive by massive public controls. Forcing people to religious services several times a day gives secret police ample opportunities to search for evidence of dissidence.
Polygamy brings about two major problems. First, government has to be oppressive enough to keep people from revolting against the concentration of wealth in ever fewer families. The second problem takes longer to surface. The children of polygamists tend to “deviate to the mean”.
Genetically, and statistically, intellects become mediocre. There aren’t any Thomas Edisons among them. Their intellectual “advances” can only come by copying the creations brought to light by the brighter, more intellectually diverse children of monogamy.
The Christian countries are hated, on the surface, for having better living conditions. Those better living conditions are the result of having smarter people freer to do what they do best. Both freedom and genetic diversity are destroyed by polygamy.
Christian countries do something else that makes polygamous countries even worse. They encourage the very smartest of their men to come to the west, where they are given high-paying jobs as physicians and engineers. That further impoverishes polygamous gene pools of all but the mediocre.
Each generation sinks farther away from the creative genius that monogamous cultures regularly produce.