One of the features of the time in which Hazrat Mahdi (as) will appear is that the Islamic world will not be one and united. The fragmentation of the Islamic world, divisions, disagreements and even conflicts between Muslim societies and groups, are one of the portents of the coming of Hazrat Mahdi (as). Hazrat Mahdi (as) will totally eliminate that division when he appears and establish the unity of the Muslim world. All Muslims will unite around Hazrat Mahdi (as) in love and joy.
Amr ibn al-Nufail says: I heard Imam Hussein say: “He whom you await [Hazrat Mahdi (as)] will not come UNTIL YOU SAY YOU ARE FAR REMOVED FROM ONE ANOTHER, UNTIL YOU SPIT IN ONE ANOTHER’S FACES AND ACCUSE EACH OTHER OF DENIAL AND UNTIL YOU CURSE ONE ANOTHER. I said: So there will be nothing auspicious at that time? He said: “No, the most auspicious of all will be during that time. HAZRAT MAHDI (AS) WILL APPEAR AND ELIMINATE ALL THESE THINGS.” (Sheikh Muhammad ibn Ibrahim Numani, al-Ghaybah al-Numani, p. 241)