Which of these could not have occurred until the post classical era a west ruler converts to islam byzantine merchant sells goods in India chinese ruler sends an ambassador to Europe Persian ruler decides to attack a greek city state

A West African ruler converts to Islam.

Explanation:

The post-classical era marked the expansion of civilizations and the development of trade. International trade developed even beyond the Silk Road, expanding to Europe, Africa, Asia. Islam started spreading based on the revelation of Prophet Muhammad in the Arabian Peninsula. Islam had a reflection of Jews, Christians, and Zoroastrians. Islam began spreading widely in Africa, Europe, and Asia due to invasions, expansions, merchants, and trade activities. Africa was the first continent to be converted to Islam. Almost one-third of the Muslims are in this continent.