In the past it was mainly under the impetus of conservative groups, including Christian organizations, which attempted to ban books. They were seldom successful.
In more recent times censorship has come overwhelmingly from the Left and they have been actually been very good at getting their way. That's because the Big Media supports them in this. They use terms like 'hate speech' as an excuse to cancel the writings of those who do not strictly adhere to identity politics, multiculturalism, and globalism.
It's gotten so bad that when doing a Google search a person is usually better off starting with the results on page two or three because the first page will invariably be filled with left/liberal/progressive takes on any subject you name.
Wikipedia is by no means immune. Its editors are overwhelmingly (more than 90%) left-liberal in orientation. Wikipedia is okay for uncontroversial subjects like the nesting habits of robins or the population of Fresno, California, but don't expect anything like objective treatment for anything that's happened in history. I don't know how deep the corruption is by I have personally been approached by one of their editors to pay to get an article on Wikipedia. The biggest problem isn't the graft, though, it's the ignorance or outright propagandizing. Facts are frequently omitted to suit a narrative. Many entries on Wikipedia change daily, as editors fight it out when two of them cannot agree.
Ultimately this is leading to a 1984 situation only much more sophisticated than Orwell imagined. The state doesn't even have to get involved! Let outraged readers and editors and owners of giant corporations alter history and ban and gag contrary opinion!
It's yet another reason to put more trust in printed material rather than books. They cannot be as easily altered or even eliminated. Yes, you can burn books. But with electronic media, the person in control only needs to hit the delete button.