But the spread of Islam into China (in reality Central Asia - there's a reason Xinjiang has historically been called Turkestan, Uyghur is the closest living lan

But the spread of Islam into China (in reality Central Asia - there's a reason Xinjiang has historically been called Turkestan, Uyghur is the closest living language to Chagatai, and why a Kashgari family has managed the Jama Masjid in Delhi for centuries) and South East Asia was itself because of Islam's prominence in Central and South Asia. The early Islamic preachers in what became Indonesia and Malaysia were South Asian or Iranian in origin, and a major reason why Persianate motifs are prominent in Southeast Asian Islam. Same with much of Central Asia. That would have not happened if the Byzantine-Sassanid War did not happen, because what became Yemen and Oman would have remained under Sassanid suzerainity and much of the Levant would have remained Byzantine. And thus, Khorasan, Gujarat, Sindh, and Punjab would have not become Muslim. That said, I agree with you that the spread of Islam was HEAVILY dependent on trade.