Burma

Burma was a nation in Asia. In the 13th century, it was under the nominal control of Kublai Khan. The First Doctor once won all its commerce for one year by playing high-stakes backgammon. (DW: Marco Polo)

Burma was never identified as a country in Marco Polo, and it certainly wouldn't have been considered one by the Khan. In real life, Burma had been captured by Kublai only two years prior to the date of the story, 1289.