"The most important political changes happened in the 1990s" In the Passive Voice?

I understand, "the most important political changes happened in the 1990s" Is in the Active Voice. Is it also possible in the Passive?

Thank you for any help.

No. There is no direct object to be the subject of a passive construction.

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Originally Posted by 5jj

No. There is no direct object to be the subject of a passive construction.

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I understand, though if the sentence were, "The most important political changes happened to them in the 1990s" would a passive construction be possible?

We don't use happen in the passive.