Genghis khan united the mongols and built and empire by combining
question 5 options:
a. samurai warriors ruling the clans.
b. shogunates within a feudal system.
c. mongol battle tactics with a belief in racial superiority.
d. a superior cavalry with a confederation of tribes and clans.

Mongolian Empire Genghis khan unified the Mongolian steppe tribes who were constantly involving themselves in fights due to an incompetent head of those nomadic tribes. Khurilitai was a tribal council which recognized Temujin Khan to be the youngest ruler and for the first time, all Mongolian steppe tribes unified into an empire.  

After unification of all tribes under one leader, the elders gave a unique name which made people quiver out of fear in future: Genghis khan.

This tribal unification created an empire which even subdued the Chinese and the empire grew vast up to Spain.

i'm not certain but i'm pretty sure it was spanish and portuguese america.