“Tartaria”??? In 1821 there was no such entity, leave alone an empire.
Tartaria: an Empire hidden by history, or revealed by ...
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Basically, some people noticed that until the 18th and 19th century, maps included a region called “Tartary” or “Grand Tartary” in the east of Russia, Central Asia and Siberia. They ally this with quotes from the Encyclopedia Britannica (an 18th century work) in articles like this one to claim that there’s a hidden Empire in history.
How hard was that?