What major event most contributed to the spread of Islam?

The major event that most contributed to the spread of Islam was the military conquests during the early Islamic Caliphates, particularly under the Umayyad and Abbasid dynasties. These conquests allowed Islam to expand rapidly across regions such as the Middle East, North Africa, and parts of Europe and Asia. Additionally, trade and cultural exchanges facilitated by these conquests helped disseminate Islamic beliefs and practices, making Islam a significant religious and cultural influence in various societies.