The statement that best analyzes the effect of leadership on the collapse of the Mongol Empire is:
"Disputes over leadership led to the fragmentation of the Mongol Empire into smaller khanates."
After the death of Genghis Khan and the subsequent leaders, the vast Mongol Empire started to experience internal disputes over succession and the distribution of power. These disputes seriously weakened the central authority and led to the empire being split into various khanates, each ruled by different descendants of Genghis Khan. Over time, these khanates became increasingly independent and often fought amongst each other, which facilitated the collapse of the Mongol Empire as a unified political entity.