You're quibbling about minor details. Khan was head of a belief system: believe and help him and you might not die. He and his men wanted the tundra cleared of cities. He did it.
nine_k says>""An empire has to be somehow tolerant towards differences between the many nations it consumes. The process of assimilation, even if forced, can and usually does take centuries."<
Khan didn't assimilate, he destroyed. Only after his death and the end of his generation of warriors, was his former empire "assimilated" by groups lucky(?) enough to be alive.
The words "tolerant" and "assimilation" have no place when speaking of the advancement of Gengis Khan's armies out of Mongolia.
Just like "faith systems" today have no tolerance, accept no "repentance" and refuse "assimilation".
An empire has to be somehow tolerant towards differences between the many nations it consumes. The process of assimilation, even if forced, can and usually does take centuries.
Faith systems are not like that: they require an immediate conversion, and an immediate and willing following the norms.