tldr: Pagan Mongol tribes

I theorize: Nomadic mongol tribes (horsemen who used bow and arrow to hunt 🏇🏹) converted quite quickly to the religion of the people they conquered. But the Mongols where mostly pagan shamanistic tribes in the beginning (they believed in the Sky god Tengri) and transferred some of their culture into ruling elites of their subject countries and killed many monotheistic farmers people greatly altering east asian and central asian demographics at a scale of 40.000.000 people 💀. Also the Mongol conquests acted as a buffer that kept Islam or Orthodox Christianity spreading beyond central asia into east asia for 500 years:

• Mongol tribes captured Moscow and beyond, preventing orthodox Christianity to expand to China faster
• Mongol empire captured the Chinese capital Beijing. Maybe their shamanistic believes influenced locals.
• Timurid (emperor Timur was grandson of Mongol Ghengis Khan) empire only expanded west not to China by their luck. They defeated mostly muslim empires like Persians and Ottomans. This prevented larger muslim expansion into east Asia. Even Europeans viewed the muslim timurids as a great threat, but also as a ally against Persian and Ottoman empires.
• The siege of Baghdad in the year 1258 by the Mongol empire with Chinese siege-craft destroyed the Muslim "golden age" destroying a chance of their expansion to east asia

Additional theory: Shamanistic Mongol tribe invasions might have deeply altered the subconscious of the religious people they annexed in central Asia/Eastern russia and Persia, what is known that they replaced the ruling elites and subtly influenced hierarchy to make taxation easier.