Can an entire country "larger than Russia" disappear?

Why have so few people heard of the country called Tartary, said to be 'larger than Russia',  which existed from the middle ages until the mid-1800's? Is it possible it has been deliberately erased from history, or is there more to this than meets the eye?

There is a growing body of evidence which shows Tartary simply disappeared from existence. This was not due to a war, since any it was involved in would certainly be well-known in world history.

Tartary had it's own flag, government and was considered a major political power as recently as the 18th century.

Quietly subsumed

"Tartary, a vast country in the northern parts of Asia, bounded by Siberia on the north and west: this is called Great Tartary. The Tartars who lie south of Muscovy and Siberia, are those of Astracan, Circassia, and Dagistan, situated north-west of the Caspian-sea; the Calmuc Tartars, who lie between Siberia and the Caspian-sea; the Usbec Tartars and Moguls, who lie north of Persia and India; and lastly, those of Tibet, who lie north-west of China."

- Encyclopedia Britannica, Vol. III, Edinburgh, 1771, p. 887.