The American Dream isn't dead. It's just moved to Denmark.

Now, we like to think of ourselves as a classless society, but it isn't true today. As the Brookings Institution has pointed out, America has turned into a place Horatio Alger would scarcely recognize: we have more inequality and less mobility than once-stratified Europe, particularly the Nordic countries. It's what outgoing Council of Economic Advisers chief Alan Krueger has dubbed the "Great Gatsby Curve" — the more inequality there is, the less mobility there is. As Tim Noah put it, it's harder to climb our social ladder when the rungs are further apart.

And it's getting worse.

Inequality is breeding more inequality. It's a story about paychecks, marriage, and homework. Now, it's not entirely clear why the top 1 percent have pulled so far away from everyone else, but there's a long list of suspects. Technology has let winners take, if not all, at least most, in fields like music; deregulation has set Wall Street free to make big bonuses off big bets (and leave taxpayers with the bill when they go bad); globalization and the decline of unions have left labor with far less leverage and share of income; and falling top-end tax rateshave exacerbated it all. But high-earners aren't just earning more today; they're also marrying each other more. It's what economists romantically call "assortative mating" — and Christine Schwartz, a professor of sociology at the University of Wisconsin, estimates inequality would be 25 to 30 percent lower if not for it.

Marriage is widening inequality today, and keeping it wide tomorrow. Well-off couples get married more, stay together more, read to their children more, and otherwise have more time and money to spend on their children's education. As the New York Times points out, economists Richard Murname and Greg Duncan have found that high-income couples have poured resources into the educational arms race at a prodigious pace the past generation. For one, the amount of time college-educated parents spend with their kids has grown at double the rate of others since 1975; for another, high-income households invested 150 percent more in "enrichment activities" for their kids from 1972 to 2006, compared to a 57 percent increase for low-income households.