A definition from answers.com An overview of differences between Portugal and the U.S. regarding 'race mixing'.
Miscegenation is an archaic neologistic term invented in 1863 to describe people of different human races (usually one European and one African) producing offspring; the use of this term is invariably restricted to those who believe that the category race is meaningful when applied to human beings. In modern usage, the term is common only among those who believe that such "race mixing" is inherently bad.
Miscegenation was a rule in the Portuguese colonization, and was even supported by the king himself. Miscegenation was considered the way to boost low populations and guarantee a successful settlement, thus settlers often released African slaves to become their wives. Some of the children were guaranteed full Portuguese citizenship, possibly based on lighter skin color, but not race. Some former Portuguese colonies are predominately mixed-race nations, for instance, Brazil, Cape Verde, and Goa. Mixed marriges between Portuguese and locals in former colonies were very common in all Portuguese colonies. Miscegenation was still common in Africa until the independence of the former Portuguese colonies in the 1970s. Until today, the Angolan, Brazilian, and Cape Verdian societies are defined by lighter skin (not race). In Cape Verde, the population is often differentiated by lighter and darker skin (known as pele de chocolate, or "chocolate skin").
The word miscegenation was coined in an anonymous propaganda pamphlet printed in New York City in late 1863, entitled Miscegenation: The Theory of the Blending of the Races, Applied to the American White Man and Negro. As the pamphlet noted, the term was coined from two words of the Latin language, miscere (to mix) and genus (race). The pamphlet argued in favor of "interbreeding" of "White" and African Americans until the races were indistinguishably mixed, and claimed that this was the goal of the United States Republican Party. The real authors were David Goodman Croly, managing editor of the New York World, a Democratic Party paper, and George Wakeman, a World reporter. The pamphlet was soon exposed as an attempt to discredit the Republicans, the Abraham Lincoln administration, and the abolitionist movement. Nonetheless, this pamphlet and variations on it were reprinted widely in communities on both sides of the American Civil War by opponents of the Republicans.
The word miscegenation entered the language in the Southern USA. For a century, it was common for white southern advocates of the social status-quo to accuse advocates of the elimination of slavery, and later the advocates of civil rights for African Americans, of actually having the goal of miscegenation and the "destruction of the white race."
One important strategy intended to discourage the practice was the promulgation of the one-drop theory, which held that any person with so much as "one drop" of African "blood" must be regarded as "black." After World War II, many white southerners accused the US civil rights movement of Martin Luther King of being a Communist plot funded by the U.S.S.R. in order to destroy the United States through miscegenation.
In most of the southern states, various laws were passed making it illegal for members of different races to marry; these were known as anti-miscegenation laws, like the South African Immorality Act. Interracial marriage was prohibited by state laws, the constitutionality of which was upheld by the U.S. Supreme Court in "Pace v. Alabama" (1883). That decision was not overturned until the United States Supreme Court ruled in "Loving v. Virginia" (1967). At that time, 16 states still had laws prohibiting interracial marriage. This case reflects the social changes at that time and will be cited as a foundation for the privacy challenges ahead regarding same-sex marriage in the twenty-first century.
Typically a felony, anti-miscegenation laws prohibited the solemnization of weddings between races and prohibited the officiating of such ceremonies. Sometimes the individuals attempting to marry would not be held guilty of miscegenation itself, but felony charges of adultery or fornication would be leveled against them instead.
Even though anti-miscegenation laws were ruled unconstitutional in the United States by the Supreme Court in 1967, those laws were not completely repealed in some states until November 2000 when Alabama became the last state to repeal its law. According to Salon.com: "In November 2000, after a statewide vote in a special election, Alabama became the last state to overturn a law that was an ugly reminder of America's past, a ban on interracial marriage. The one-time home of George Wallace and Martin Luther King Jr. had held onto the provision for 33 years after the Supreme Court declared anti-miscegenation laws unconstitutional. Yet as the election revealed -- 40 percent of Alabamans voted to keep the ban -- many people still see the necessity for a law that prohibits blacks and whites from mixing blood."
An example of how anti-miscegenation laws were enacted can be seen during the 1930s, when the racist and anti-Semitic Nuremberg Laws were enacted by the Nazis in Germany against the large German Jewish community, forbidding marriages between the Jews (deemed as Untermenschen - "lower people") and German Aryans (deemed the Übermenschen - "higher people"). Many interfaith and intermarried couples committed suicide when these laws came into effect.