From the military juntas that ruled Argentina and Chile in the 1970s and 1980s to Joseph Stalin's iron-fisted regime in the Soviet Union, dictatorships have a long history of making their detractors "disappear." Today, this sinister practice seems to be making a comeback.

Under the military regimes in Chile or Argentina, a person might be tossed into the sea from a helicopter, never to be found. They might be killed and then burned beyond recognition or coated in lime, to accelerate decomposition, and buried in an unmarked grave.

In Stalin's Soviet Union, someone could be picked up and taken to the Lubyanka (the KGB headquarters) or some other nightmarish facility at any moment. During the purges of the 1930s and later, members of the Communist Party were particularly vulnerable, and millions of Soviet citizens disappeared forever in prisons or the gulag.

Today, modern authoritarians are reviving such behavior, suddenly and covertly snatching people, including well-known figures and high-ranking officials, to be detained or worse. In many cases, the "vanished" do eventually resurface, but with an apparently transformed perspective on their past work or the government that detained them. Here, China and Saudi Arabia stand out – though they are by no means alone – for orchestrating a series of increasingly brazen abductions or vanishings of their detractors.