this verse of Quran says if two group of Muslims fought each other, Muslims should fight against the Baqiyah group. but problem is usually both group claim the other side is Baqiyah group. according to this verse we as Muslims should fight to Baqiyah group. so how the baqiyah group should be determined?
وَإِن طَائِفَتَانِ مِنَ الْمُؤْمِنِينَ اقْتَتَلُوا فَأَصْلِحُوا بَيْنَهُمَا ۖ فَإِن بَغَتْ إِحْدَاهُمَا عَلَى الْأُخْرَىٰ فَقَاتِلُوا الَّتِي تَبْغِي حَتَّىٰ تَفِيءَ إِلَىٰ أَمْرِ اللَّـهِ ۚ فَإِن فَاءَتْ فَأَصْلِحُوا بَيْنَهُمَا بِالْعَدْلِ وَأَقْسِطُوا ۖ إِنَّ اللَّـهَ يُحِبُّ الْمُقْسِطِينَ
[49:9] Sahih International
And if two factions among the believers should fight, then make settlement between the two. But if one of them oppresses the other, then fight against the one that oppresses until it returns to the ordinance of Allah. And if it returns, then make settlement between them in justice and act justly. Indeed, Allah loves those who act justly.
it is possible to such war happen in our time. for example Iran/Iraq war happened in some year ago between two Muslim nation. so we should know how to determine Baqiyah group.
for example consider the Camel war in history of Islam that near 20,000 Muslims were killed in this war. and assume it happen now in our time with the same leaders (Imam Ali S.A in one side and Aisha and Talha and Zubar in other side). then:
1- according to above verse is it obligatory for Muslims to participate in this war?
2- if yes, how to determine which side is Baqiyah group.
3- according to your method for determining Baqiyah group which side was Baqiyah side in Camel war?