When I lived in Montreal in the 1980s, Canadians had an expression for the lack of contact between the French-speaking and Anglophone communities. They called it the "two solitudes".
After spending the past three years in Washington, that's how I would describe one of the most striking features of American society. Segregation has gone, mercifully consigned to the dustbin of history, but African Americans and white Americans still live separate lives.
I first started thinking about the myth of the American "melting pot" at a baseball game of the Washington Nationals. They were languishing at the bottom of the league table but 2010 saw the astonishing debut of pitcher Stephen Strasburg, and suddenly there was a buzz about the team which this year made it through to the play-offs after a momentous season. As I looked around the stadium, there was not a single black face among the spectators.
A couple of weeks later, I went to a Washington Capitals hockey game. There again, the same thing: all the spectators were white. This surprised me all the more because the population of the nation's capital is predominantly black.
At other cultural events, at the movies, in restaurants and bars or even at a theatre established among a predominantly black community, I would only ever see white Americans. It struck me that the last time I had seen African Americans in an audience was in 1995 at a cinema in New York showing the black romantic comedy Waiting to Exhale.
Gentrification has clearly played a role. I can remember when I lived in New York and my subway train reached 96th St on the east side of Manhattan, the conductor would yell out "last stop for the whites". These days, white New Yorkers and a surging Hispanic community have moved deep into Harlem, whose Congressional district now boasts more Latinos than blacks in a historic transformation.
In my neighbourhood of Eastern Market in Washington, a stone's throw from Congress, "yummy mummies" with pushchairs have replaced the drug pushers and professional white families have moved into houses that were crack dens 10 years ago. The black community, pushed out by rising prices, went further east and across the river in Anacostia.
If you drive across Washington from northeast to northwest, the racial and ethnic make-up of each community is obvious from the car occupants, with the black faces vanishing as fast as you can say Dupont Circle.
I can't say I ever noticed any hostility between blacks and whites. Yet opinion polls say that the presidential campaign was the most racially charged in three decades. A spokesman of the Republican campaign for Mitt Romney, John Sununu, kicked up a political storm by suggesting that former Secretary of State Colin Powell had only endorsed President Barack Obama because both men were black.
Demographic analyses of the presidential election results confirmed the racial cleavage, which I saw for myself.
At a rally in Virginia for President Obama, I saw blacks, whites, Asians and Hispanics, all sitting together. Two days later, at a Romney event only a few kilometres away, only white people showed up.
I asked Peter Salins, a distinguished American political scientist who wrote Assimilation, American Style, whether the "melting pot" had ever existed. He says that it depends on how you define it. The real test is social harmony rather than my cultural observations. And based on that criterion, he sees a definite trend towards assimilation. Eventually, says Salins, culture catches up.
He points out that "the assimilation paradigm never took hold in the African American community" descended from slaves. "But that's eroding now, it's slowly being solved. With each generation there will be more middle class blacks".
As for the Hispanic community, which has now overtaken the black population as the dominant minority, they start out living in separate "barrios" and speaking Spanish at home, "but in one or two generations they will be unrecognisable as Hispanics other than in name"
And there is one big factor demonstrating the enhanced levels of racial tolerance in the US: the election and re-election of Obama, the country's first black president. So, "I wouldn't worry about baseball games," said Salins with a laugh. And on that hopeful note, I'm leaving Washington.
Anne Penketh was the Herald's Washington correspondent from 2010 and is now based in Paris.