Ḥaḍrat Ḥajī Imdād Allah Muhājir Makkī used to say that the foundation for unity is humility. If each person was to think himself inferior than every other person then the possibility of any disunity would not even arise. This is because disunity only ever comes about due to one person thinking himself better than another. Such a person then tries to upstage and surpass others (hence creating disunity).
(Ahl-e Dil ke Anmol Aqwāl, pg:49)