Genghis Khan hadn’t committed his first murder (his half-brother) or mass-murdered his first rival tribe until the Silk Road was more than 1200 years old.
Oh sure, there’s that. But if not for Ghengis and his progeny, the black death would never have decimated Europe. :{)
The Silk Road repeatedly opened and closed over the centuries depending on the vagaries of conquest along the route.
Given the enormous transport costs and risks, only the very highest value and lowest weight/bulk goods could be traded this way.