Those three words became kind of a trope starting I'd say in the 1980s when the dissolution of the Soviet Union, the rise of Reaganomics, the remaking of the Democratic Party into a Wall Street adjunct of identity politics sects, and the Postmodern rejection of ideology in general caused the Marxist analysis to fall into more or less disfavor among academics and at popular intellectually leaning publications like The Nation magazine.
Of those three words, class refers to the Marxist analysis, but the other two meant that everything had also to be put through race and gender analysis. Gender analysis means,loosely, a Feminist analysis, but feminism is a wiggly term and in common parlance it means identity politics that promotes the interests of women. The same with the term "race." There's a white supremacy critique that's similar to the critique of patriarchy, but commonly we're talking about identity politics again that promote the interests of Black people. The problem with identity politics is that it simply seeks to rearrange where you sit on the totem pole. It only seeks to rearrange the hierarchy of power and privilege that are functions of economic status. In other words, of class. If you don't deal with that, if you leave the system in place that reproduces economic class, you might have another group sitting on top, but they will behave the same as the one that's there now. Why? We're all human. We're equal. We're the same species.
I say all this to introduce an article that just appeared in the The Nation that makes the case for racial discrimination -- race -- being a function of class oppression. (Marxism holds that the same can be said of gender discrimination.) The article doesn't explicitly say it's based on a Marxist analysis, but it is. That's The Nation's DNA, brought to the surface again, apparently, by the rise of economic populism, which began with Occupy Wall Street but has become more mainstream now because of the Bernie Sanders candidacy. Those who thought Occupy was a flash in the pan spoke too soon. It was only the initial expression of peoples' discontent at 40 years of Reaganomics, growing economic inequality and employment insecurity, and a recovery that was benefiting only a few people. Socialism is not only in the DNA of The Nation, though. It's appeared in various forms throughout history. It's an expression of our innate sense of fairness and our natural human impulse for compassion that exist alongisde the more base instincts that are expressed through systems like Capitalism. It's the same sentiment expressed by whoever wrote the Sermon on the Mount. You see it surfacing everywhere, increasingly, again; in the fact that "Socialism" in the course of just about a year has lost almost all its force as an epithet, in the fact that more young voters in Iowa identify as "Socialist" than as "Capitalist", and in appearance of increasingly more articles like this one.