In the century after the foundation of the United States, no fewer than thirty-eight states banned interracial marriages. In 1915, twenty-eight states retained such statutes; ten of them had gone so far as to make the prohibition on miscegenation constitutional. There was even an attempt, in December 1912, to amend the federal constitution so as to prohibit 'forever . . . intermarriage between negros or persons of color and Caucasians . . . within the United States'. The language of the various statutes and constitutional articles certainly changed over time, as rationalizations for the ban on interracial sex evolved, and as new threats to racial purity emerged. Definitions of whiteness and blackness became more precise: in Virginia, for example, anyone with one or more 'Negro' grandparents was defined as a 'Negro', but it was possible to have one 'Indian' great-grandparent and still be white in the eyes of the law. Depending on patterns of immigration, a number of states extended their prohibitions to include 'Mongolians', 'Asiatic Indians', Chinese, Japanese, Koreans, Filipinos and Malays. Penalties also varied widely. Some laws simply declared interracial unions null and void, depriving couples of the legal privileges of marriage; others specified penalties of up to ten years in prison. Nevertheless, the underlying motivation seems remarkably consistent and enduring.
Niall Ferguson, The War of the World: Twentieth-Century Conflict and the Descent of the West (2006), p. 21