There was this Quora question about why Genghis Khan was so successful. Here’s the answer:
The insane execution of meritocracy and discipline in his armies.
The “organization” he led was constructed so perfectly that no other military force at the time could go head to head. There were contenders though, they were defeated, harshly.
Let’s talk about meritocracy first, and this is the main reason why Mongol made an empire run across Eurasia.