One might wonder how come these nomads can make such high scores, but I assure you somebody so dumb and weak would never rule the half of the world for centuries and prove their physical and brain power. This was not a job for dummies.
From the other point of view, Mongols can be called real "dumb" if you consider the situation we are now in. Once a nation made a name in the world history, Mongols ended up being the poorest and weakest place on earth without being able to protect themselves on their own. And develop as a country, really!
What has led to this , let me call it tragic, situation? Nothing but the internal wars lasted for years and years after Mongol Empire's collapse. Chinggis Khaan united all the warring Mongol tribes once, but his sons and grandsons and later khaans (kings) ruined the country fighting against each other for power and wealth with a result losing all together at the end.
So what was left after all this? A country with a population near to extinction and plagued by stupid Tibetan Lamaism which brought nothing but "useless" lamas residing at many temples and for whom marriage was a taboo, thus "contributing" their share to the reduction of the population. We should thank the God that we could keep the most part of the homeland today called Mongolia. Now it is time to rise for us and despite the lower number of people, compared to many nations, we are able to compete at the world level. And this ranking on National IQ score shows our capability.
Countries are ranked highest to lowest national IQ score.