There is no dearth of events in history when two or more groups of Muslims have been fighting among one another. It is natural to have differences. However, in some cases, differences have led to fighting among different groups of Muslims. Allah guides us in the Quran that Whenever (unfortunately) two groups of Momineen fight each other, a neutral body / central authority should make peace and reconciliation between them.
وَإِنْ طَائِفَتَانِ مِنَ الْمُؤْمِنِينَ اقْتَتَلُوا فَأَصْلِحُوا بَيْنَهُمَا فَإِنْ بَغَتْ إِحْدَاهُمَا عَلَى الْأُخْرَىٰ فَقَاتِلُوا الَّتِي تَبْغِي حَتَّىٰ تَفِيءَ إِلَىٰ أَمْرِ اللَّهِ فَإِنْ فَاءَتْفَأَصْلِحُوا بَيْنَهُمَا بِالْعَدْلِ وَأَقْسِطُوا إِنَّ اللَّهَ يُحِبُّ الْمُقْسِطِينَ
إِنَّمَا الْمُؤْمِنُونَ إِخْوَةٌ فَأَصْلِحُوا بَيْنَ أَخَوَيْكُمْ وَاتَّقُوا اللَّهَ لَعَلَّكُمْ تُرْحَمُونَ
Sura Al-Hujrat (49), verses 9-10.
In the light of Sura Al-Hujrat (49), verse 9-10, there should be an Islamic Peace Force (IPF) among from the members of the Organization of Islamic Countries (OIC). It should be supported by an Islamic Peace and Reconciliation Political Wing (IPRPW). All internal disputes among various factions of the Muslims should be resolved by the IPF and IPRPW.
Consider for example, the current situation in Syria, Afghanistan and the fighting with Taliban. Had there been any force such as IPF, there had been no need for intervention from the NATO or other external forces. Muslims, themselves, could have sorted out their internal disputes.