I have this notion of my own that the world has experienced four (and maybe now five) great outbursts of this symbiosis between conspiracism and counter-conspiracy in the past century: 1920s Russia, 1940s Germany, 1960s China, 1980s Iran, and, just maybe, 2000s USA. One might hope that this latest iteration is a little gentler in its outcome, being based more on DIY Internet theorizing than on demagogic mass media.
For a country to be on your list, as I understand it, that country's government must make its major policy decisions based on indefensible conspiracy theories. Is that what you meant?
The list itself is of interest. Cambodia under the Khmer Rouge would seem to fall squarely with the others, and perhaps even to be the epitome of this human failure.
For the first four, maybe, but not for the fifth (one reason why I stumbled over its inclusion). What these "great outbursts" are supposed to have in common is world-historical significance, which in every case except 1980s Iran means that a great power is involved. As for the Khmer Rouge, if I were to write a history of the past century organized around these five outbreaks, I'd make them a postscript to "1960s China".
When we get to the present day, I'm not convinced that my fifth item warrants inclusion. Both sides of American politics on occasion accuse the other of conspiracy and of baseless conspiracy theorizing, but this is a chronic condition of politics in all societies. I think what has happened is that a certain type of conspiracy - stealth WMD attacks by an invisible enemy - has become the threat around which the world is reorganizing, and so the conspiracist dimension of politics has become central in a way that it wasn't before. Thus people argue about whether Iraq sponsored al Qaeda, whether Iraq sent the anthrax, whether the Bush administration cynically promoted these ideas in order to engineer the war, whether they fell prey to conspiracist thinking and fought the wrong war, whether the anthrax was meant to frame Iraq or to stimulate biodefense research, etc. Perhaps one can similarly find a structural reason why conspiracism became prevalent and relevant on those earlier occasions too.