As the 1990 film describes the process, a small cadre of religious men led a military coup to take-over what they increasingly viewed as a Godless country. Because wide-spread sterility had set in, these men believed that God had sent America a "plague of barrenness, a desert of infertility."
God's reasoning, they surmised, was that the Lord didn't approve of abortion, birth control, artificial insemination, test tube babies, or homosexuality. These men thus usurped control of the United States, relegated minority citizens to death camps, made homosexuality a "gender treachery crime," and greatly curtailed the rights of women, particularly fertile women.
In the future imagined by The Handmaid's Tale (1990), the rich, white elite have gamed the system to consolidate political and personal power. These upstanding "Christian" men stride atop of the society's food chain while their infertile wives are left at home (with ample servants) to pine away for children and motherhood. Meanwhile, these same men can lawfully engage in sex with fertile "handmaids" so as to conceive children.
Where do these handmaids come from? Well, from anywhere the men can get them, even if the fertile women are already mothers and wives in other, less fortunate families.
Family values only matter, you see, if it's your family that you value.
"We are weeding out the Godless."