It is hard to know how much of the difference between Khubilai Khan and his grandfather, Chinggis Khan, was caused by circumstance and how much by innate differences in their respective personalities and sets of talents. However, the two men were rather different. The major difference was that Chinggis was something of a ruthless conqueror while Khubilai was more of a ruler and governor.
Chinggis Khan was, of course, the first Mongol leader to unite the various Mongol tribes and make them into a strong and consolidated group. At the head of this consolidated group, he was the first Mongol leader to engage in widespread conquest. As he was almost 40 years old before he even consolidated the Mongol tribes, this conquest was his major life’s work (he died when he was about 60).
From what your text tells us, we can see that Chinggis was a ruthless conqueror when he needed to be. We see that he essentially destroyed every city of the Khwarazm shah when that ruler refused his diplomatic advances. He even destroyed the irrigation system that the Persians had built in that region, making agriculture much more difficult in that area. Using tactics such as this, Chinggis conquered a huge area of land, building the foundation for the Mongol Empire. However, as Bentley and Ziegler say on p. 272 of the Brief Second Edition, “Chinggis Khan was a conqueror, not an administrator.”
This is where the major difference between Khubilai and Chinggis lies. Chinggis lived at a time when the Mongols did not control a vast area. His goal was to conquer and control as much as he could. By contrast, Khubilai lived at a time when the Mongols already dominated large areas. He was, therefore, less of a conqueror. He did extend Mongol rule to some degree, but his main goal was not conquest. Instead, his main goal was making sure that the Mongols could successfully rule in China (his part of the empire). He was more of an administrator and ruler where his grandfather was more of a conqueror.