Segregationist schools lost their tax exempt status if they continued to deny enrollment to black kids, so they banded together to form the Religious Right. Then, because they knew that the message "Keep Blacks Out of Our Schools" wouldn't resonate well across the rest of the country, they brainstormed for wedge issues which would play well with Christians everywhere. Abortion was one of those issues, of course, though prior to the 70's most Christians considered it an issue of law, not religion. The Religious Right was a natural ally for the Republican Party as it transformed from fiscally conservative to morally conservative, and continues to be to this day. All because some shitty people didn't want to let black kids mix with white kids in school.