In one of his most important lessons, he told his sons that conquering an army is not the same as conquering a nation.
You may conquer an army with superior tactics and men, but you can conquer a nation only by conquering the hearts of the people.
As idealistic as that sounded, he followed with the even more practical advice that even though the Mongol Empire should be one, the subject people should never be allowed to unite as one:
“People conquered on different sides of the lake should be ruled on different sides of the lake.”
Like so many of his teachings, this, too, would be ignored by his sons and their successors.
'Genghis Khan and the Making of the Modern World' by Jack Weatherford
https://www.amazon.com/dp/B000FCK206