What was the cause of the alliance between the Muslims at the beginning of the Hijrah?

Question:
The cause of the alliance?

Answer:
It is what was mentioned earlier: it is the renewal of mutual support and the affirmation of mutual support against the common enemy. These people came to them from lands other than their own, and they were the Muhajirun (Emigrants), so it was feared that there might be estrangement or division. So the Prophet (peace and blessings be upon him) established brotherhood between them, such that they were brothers in Allah; this one is the brother of that one, and that one is the brother of this one. There was love between them, and mutual support, and mutual inheritance. They were more entitled to this than their relatives. Then, this ruling was abrogated.
Q: Was the abrogation general?
The Shaykh: Yes, the abrogation was general. What remains is only the affection of Islam, the love of Islam, and the loyalty in Islam. As for inheritance, it is for one's relatives and in-laws.