Shaykh Al Islam Ibn Taymiyya mentioned the madhhab of the fuqaha. That is that if all of the muslims are united under one leader, then dividing the muslims is haram. However if the muslims are already split up under different rulers and dynasties, everybody has to obey the ruler of their country and withhold from rebelling against him. This division has existed since the martyrdom of Uthman Ibn Affan رضي الله عنه.
