Progress -- which was God's great work, or was perhaps the real name of God -- could be defeated by inter-racial marriage.
The opponents of mixed marriages dispensed with fine distinctions; they opposed any mixing of races or genes, which they called miscegenation. And they wrote laws to ban the practice.
In all, 30 states passed anti-miscegenation laws that stayed on the books until the advent of the civil rights movement. Of these, 16 kept their laws on the books until the Supreme Court threw them out in 1967: Alabama, Arkansas, Delaware, Florida, Georgia, Kentucky, Louisiana, Mississippi, Missouri, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia and West Virginia. Another 14 states passed anti-miscegenation laws, but repealed them in the 1950s or 1960s: Arizona, California, Colorado, Idaho, Indiana, Maryland, Montana, Nebraska, Nevada, North Dakota, Oregon, South Dakota, Utah and Wyoming.
For example, Virginia's Racial Integrity Act of 1924 made it "unlawful for any white person in this state to marry any save a white person, or a person with no other admixture of blood than white and American Indian." In writing the statute, one of the challenges that the Virginia racists faced was their own proud history. According to a publication from the Registrar of the State Bureau of Vital Statistics, the law had to take account of "the desire of all to recognize as an integral and honored part of the white race the descendants of John Rolfe and Pocahontas." Because of the Pocahontas loophole, you could have a little Indian blood (one great-great-grandparent) and still be counted as white. But "every person in whom there is ascertainable any negro blood shall be deemed and taken to be a colored person."
The law automatically voided all marriages between whites and blacks. The law prohibited leaving the state to get married and then returning, and specified that the "fact of their cohabitation here as man and wife shall be evidence of their marriage." The penalty was stiff: "If any white person intermarry with a colored person, or any colored person intermarry with a white person, he shall be guilty of a felony and shall be punished by confinement in the penitentiary for not less than one nor more than five years."
Virginia judges continued to defend anti-miscegenation laws for decades. In 1955, the State Supreme Court of Appeals decided that the laws served legitimate purposes, including: "to preserve the racial integrity of its citizens," and to prevent "the corruption of blood," "a mongrel breed of citizens," and "the obliteration of racial pride."
http://www.eugenics-watch.com/roots/chap07.html