Intermarriage has been rising in the United States steadily since about 1960. Before 1960 there were so few interracial marriages in the United States that Interraciality was really invisible. Prior to 1960, the idea of marrying someone from another race in the US was so unusual that social pressure, family pressure, and in some states the law made such marriages impossible.
So what explains the rise in interracial marriage?
One answer is that the law changed. In 1967, the US Supreme Court, in a brief but powerful and unanimous decision (Loving v. Virginia), struck down all the state laws that had made interracial marriage illegal. Overnight, Americans had the right to marry anyone from the opposite sex regardless of race. New York, however, was one of the states that had never had laws against interracial marriage. Take a look at this map of US states to see which states had laws against interracial marriage and when.
In the above graph (click to enlarge), you can see that intermarriage had a similar rise in the US, in Brooklyn, and in New York, starting near zero, and peaking at between 5% and 7% of all marriages in 2010. The trajectory of interracial marriage was so similar in Brooklyn and in the US as a whole that the blue US line is hidden underneath the green Brooklyn line in parts of the graph above. Since interracial marriage was always legal in Brooklyn but often illegal in the rest of the US before 1967, something other than the law (which never changed in Brooklyn) must explain the rise of intermarriage.
Even though interracial marriage has risen a great deal, Americans and Brooklynites still have a strong tendency to marry people from their own racial group.
If marriages in Brooklyn were completely random with respect to race, we might expect about 70% of all Brooklyn marriages to be interracial, instead of the 6% that actually are interracial today. Brooklyn is very racially diverse: among married Brooklynites 46% are white, 22% are black, 16% are Asian, and 15% are Hispanic. Brooklyn’s high degree of racial diversity would make racial intermarriage spectacularly high (under the very unrealistic assumption of random mixing). Of course, if 70% of all couples were interracial, meaning husband’s race and wife’s race were completely uncorrelated, we would be living in a world in which race no longer mattered and nobody would think of themselves as being married to someone of another race, and nobody would think of themselves as having a race, and surveys would have long since stopped asking about race. We are a long way from that completely post-racial society. The barriers to racial intermarriage have been declining for 50 years in the US, and yet race is still the deepest division in the marriage market. Americans are still much more likely to marry someone of a different religion or a different social class than they are to marry someone of a different race. Race may be less important than it once was, but race is still today and will be for the foreseeable future one of the most important and fundamental aspects of American life.
The 6% of marriages that are interracial in the US includes all married people at the time of the census, and that means it includes married people who were married 50 years before the census, as well as people who were married the day before the census. The census is what social scientists refer to as a “prevalence” rather than an “incidence” sample. Prevalence samples change slowly, because people who were married long ago (and whose marriage reflects the trends and customs of the past) remain in the sample, as they remain part of our society.