https://en.wikipedia.org/wiki/Tartarian_Empire

Tartarian Empire
Tartarian Empire refers to a group of pseudohistorical conspiracy theories, including ideas of a "hidden past" and "mud floods" which originated as pseudoscientific Russian nationalism. Tartary or Tartaria is a historical name for Central Asia and Siberia. Conspiracy theories assert that Tartary or the Tartarian Empire was a lost civilization with advanced technology and culture. This ignores the well-documented history of Asia, which Tartary refers to.[1] In the present day, the Tartary region covers a region spanning from central Afghanistan to northern Kazakhstan, as well as areas in present Mongolia, China, and the Russian Far East in "Chinese Tartary".
Background
The theory of Great Tartaria as a suppressed lost land or civilization originated in Russia, with aspects first appearing in Anatoly Fomenko's new chronology in the mid-1970s and early 1980s, and then popularized by the racial occult history of Nikolai Levashov. In Russian pseudoscience, known for its nationalism, Tartaria is presented as the "real" name for Russia, which was maliciously "ignored" in the West.[2][3] The Russian Geographical Society has debunked the conspiracy theory as an extremist fantasy, and far from denying the existence of the term, has used the opportunity to share numerous maps of "Tartary" in its collection.[4] Since about 2016, conspiracy theories about the supposed lost empire of "Tartaria" have gained popularity on the Internet, divorced from its original Russian nationalist frame.[5]
Conspiracy theory
The globalized version of the conspiracy theory is based on an alternative view of architectural history. Adherents propose that demolished buildings such as the Singer Building, the original New York Penn Station, and the temporary grounds of the 1915 World's Fair were actually the buildings of a vast empire based in Tartary that has been suppressed from history. Sumptuously styled Gilded Age buildings are often held out as really having been built by the su…