If the Qur'an talks about the unity of Islam- and it does- that unity is the system of Mahdi. Does the Qur'an say that Muslims will unite and Islam will prevail in the whole world? It does. That is the system of the Mahdi. That is because what will be the main issue when Hazrat Mahdi(pbuh) comes. It is to ensure that Islam will prevail in the world. - Harun Yahya