“Disappeared” in the sense used here refers to domestic opponents being covertly kidnapped—and usually murdered—by their governments; a usage that originated in connection with Argentina's “Dirty War”, but which has been used for many other situations since.

The use of “disappeared” this way here I would say I is very conscious commentary in itself.

Check the details on that ngram, it doesn't capture "disappeared" as a transitive verb. Virtually all the examples are variations on "Once the item had disappeared, it was never seen again."