As Porphyrogenitus explains, enforced belief may have started with State Theistic Religion, but it soon moved on:
In [the American colonists'] experience, government-enforced belief came in the form of a State Theistic Religion. So they enshrined within the Constitution the Establishment Clause, as part of the Amendment intended to guarantee that liberty of thought and expression would be respected (note today that “freedom of expression” is commonly described to be one of the things protected by the First Amendment; there is some double-think here, because it extends only to certain kinds of expression). This was to prove a profound mistake.No sooner had the Constitution been ratified than the first non-theistic State Religion was created, in Revolutionary France, complete with its own calendar, holidays, ideology, and a non-theistic inquisition in the form of revolutionary terror aimed at enforcing this belief on those deemed unsuitably enthusiastic about it, including inevitably supporters who weren’t seen as fanatical enough (thus the end of Robespierre, hoisted on his own petard).
Enforced belief is nothing if not as jealous of rivals as Hera, so during the French Revolution Christianity was driven from the public square. That revolution foundered as a result of the bloodbath it produced, but its legacy lived on, and it would not be the last non-theistic (as opposed to atheistic, though some are) State Religion. What was Fascism and Nazism if not enforced beliefs? Or Communism in the Soviet Union and Maoist China (and even now, potential rival religions are kept to state-tamed/approved versions, or driven underground).
Today America has a set of enforced beliefs, increasingly fanatical and intolerant of rival views (ironic from a belief set that ostensibly teaches tolerance, but in reality is only tolerant of differences it itself claims are superficial — race, sex, sexual orientation). Its roots, the roots of Progressivism, are tied to a branch of Christianity, and indeed it’s origins are from New England’s Puritan Roots (thus it’s popularity on Harvard). Ethnic Studies Departments and the like are nothing if not Faith-Based Initiatives, valued not for their scholarly worth but as ideological proving grounds. Similarly, ethnic organizations (on campii and outside of it) serve not merely as social organizations, but as enforcers working in collusion with administrative power to punish those who stray into heresy.
Coincident with the Warren Court decisions on “Separation of Church and State”, a balderization of the First Amendment that gets us what we have now, this belief-set dropped its explicitly Religious ties and “secularized” (though it is still widespread among many mainline Protestant churches — such as the ones I went to — the “Liberation Theology” branch of Catholicism, Trinity United/Black Nationalist theology &c). This was not a conscious move, but a subconscious one, to give Progressives a tool to which to hound their still-Theistic rivals and initiate what amounts to a wave of (relatively mild, but still powerful) persecution, and also introduce the sort of religious indoctrination the 1st Amendment was intended to prohibit into schools, universities, workplaces, &c. Any time you receive “diversity counseling” or are taught multiculturalism (I have nothing against other cultures — as a historian, how could I? But in reality, “Multiculturalism” ends up meaning not having to know anything about other cultures, simply projecting Progressive beliefs upon them and describing them all as communal, consensus-based, peace-loving, &c &c. Scratch the surface of 95% of Multiculturalists, and they know next to nothing beyond the superficial about any actual civilization).