According to Ibn Sad, one of Muhammad's companions, the opposition in Mecca started when Muhammad delivered verses that condemned idol worship and polytheism. However, the Quran maintains that it began when Muhammad started public preaching.
Among the first things Muhammad did to ease the longstanding grievances among the tribes of Medina was draft a document known as the Constitution of Medina, "establishing a kind of alliance or federation" among the eight Medinan tribes and Muslim emigrants from Mecca. The document specified rights and duties of all citizens and the relationship of the different communities in Medina (including between the Muslim community and other communities, specifically the Jews and other "Peoples of the Book"). The community defined in the Constitution of Medina, Ummah, had a religious outlook, also shaped by practical considerations, and substantially preserved the legal forms of the old Arab tribes.
The first group of pagan converts to Islam in Medina were the clans who had not produced great leaders for themselves but had suffered from warlike leaders from other clans. This was followed by the general acceptance of Islam by the pagan population of Medina, with some exceptions.
When Muhammad was in Mecca he faded opposition but was accepted when he got to Medina making the da'wah more far-reaching.