I have used the word tribe to describe the American cultural groups, including its political factions. I have made a point of including liberals in that primarily because they deny it. Perhaps the phrase special-interest group would serve better to describe progressives.
To themselves, liberals see their ideology as more a cast of mind, an attitude. They see liberalism as a viewpoint, almost a character, that others possess in greater or lesser degree. They are tolerant - in the fashion of adults very patiently teaching children or primitive peoples what is good for them; they respect learning per se - except that is no longer true; they are generous - particularly when it comes in the form of inducing the government to distribute funds to good things. Their characters are not devoid of these good characteristics - many are indeed tolerant, generous, and respectful of learning. But they do not see how these virtues are slowly poisoned by other attitudes, until they become net negatives for those around them. One can almost identify liberal ideas by this method - excellent ideas which left things worse off as the unforeseen negatives slowly gained ascendancy. Vietnam is a good example; the United Nations another; affirmative action is still a net positive for middle-class and upper-class blacks, and so thus perhaps good for intergroup comity and the nation as a whole. But black poverty has not remitted.
These negatives are often embedded in the special interest advantage of policies that progressives prefer. They may indeed believe that these are policies that make a better society, and are good for all of us, particularly the downtrodden. Heck, the policies they prefer might even be better, though that's another discussion. But there is no getting around that the growth of government occurs in specific areas, and these areas mean more jobs for liberals - directly, as in government, or indirectly in universities, nonprofits, and government-watching media. New regulations mean new regulators; student aid means professors; new services mean new service providers. A class of people benefit. I don't say that they vote only their own self-interest. I do say that like all moralists in government they are completely unaware that self-interest enters into the equation at all.
There is not only wealth, but status that derives from cultural dominance as well. That is more subtle, but just as powerful, and very much in evidence in progressive advocacy.