Native American autonomy and agency, African Americans obtaining land after the Civil War or stimulus measures after the Great Depression, Communism... Of course, the combination of limiting free speech for decades leads to the death of the ideology because no one picks it up.

> Native American autonomy and agency, African Americans obtaining land after the Civil War

Unfortunately these were suppressed with violence, far more than mere censorship. I don't think these causes are dead at all, however. Many Native Americans still pursue these goals and occasionally enjoy victories, while the other cause has changed with the times and shifted focus from land to a more vague idea of reparations.

> stimulus measures after the Great Depression, Communism

I don't think those are dead at all. They may not be especially popular among normal people, but one can certainly get elected and openly preach violent revolutionary ideology like "We are coming to dismantle this deeply oppressive, racist, sexist, violent, utterly bankrupt system of capitalism, this police state. We cannot and will not stop until we overthrow it and replace it with a world based instead on solidarity, genuine democracy, and equality – a socialist world." [0] The organizers of BLM have explicitly stated that they are "trained organizers, trained Marxists" in the context of BLM's having adequate ideological direction. [1][2]

[0] https://www.socialistalternative.org/2020/07/07/kshama-sawan... [1] https://www.youtube.com/watch?v=jDqObO44e9s [2] https://therealnews.com/pcullors0722blacklives