I have long questioned whether Hidden Empire was an original Pelley Publication. The only Pelley copy I had seen was dated circa 1938 while there was an Oregon edition from 1936, leading me to believe the pamphlet was composed by someone else and submitted to Pelley, much as with World Hoax. Well, here is the cover of an earlier Pelley edition which may date as early as 1935, making for the possibility that it was an in-house affair. I don't believe the writing style is that of Pelley's, however.
You can read Hidden Empire here: https://archive.org/details/HiddenEmpirePelley