Why Did Al⁠-⁠Qaeda and ISIS Split

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Question:

If both Al-Qaeda and ISIS are Sunni, why did they split? - A historical explanation of the ideological and strategic differences between Al-Qaeda and ISIS, leading to their split. :::

Answer:

This is due to the wickedness of their condition and also a Mercy from God almighty because had these terrorists (having khawariji ideology)) not fought among themselves & united then the corruption on earth would not have been limited to few countries, as renowned Islamic scholar & Salaf (pious predecessor) had stated years back:

Wahb ibn Munabbih, Born - AH 34 (654/655) [Wahb ibn Munabbih - Wikipedia] said:

أني قد أدركت صدر الإسلام فوالله ما كانت للخوارج جماعة قط إلا فرقها اللَّه على شر حالاتهم وما أظهر أحد منهم رأيه قط إلا ضرب اللَّه عنقه وما اجتمعت الأمة على رجل قط من الخوارج ولو أمكن اللَّه الخوارج من رأيهم لفسدت الأرض وقطعت السبل وقطع الحج من بيت اللَّه الحرام وإذا لعاد أمر الإسلام جاهلية حتى يعود الناس يستغيثون برءوس الجبال كما كانوا في الجاهلية وإذا لقام أكثر من عشرة أو عشرين رجلا ليس منهم رجل إلا وهو يدعو إلى نفسه بالخلافة ومع كل رجل منهم أكثر من عشرة آلاف يقاتل بعضهم بعضا ويشهد بعضهم على بعض بالكفر حتى يصبح الرجل المؤمن خائفا على نفسه ودينه ودمه وأهله وماله لا يدري أين يسلك أو مع من يكون

I knew the early period of Islam. By Allah, the Kharijites never had a group except that Allah caused it to split due to their evil condition. Never did one of them proclaim his opinion except that Allah caused his neck to be struck. Never did the Muslim nation unite upon a man from the Kharijites. If Allah had allowed the opinion of the Kharijites to take root, the earth would have been corrupted, the roadways would have been cut off, the Hajj pilgrimage to the sacred house of Allah would have been cut off, and the affair of Islam would have returned to ignorance until the people would seek refuge in the mountains as they had done in the time of ignorance. If there were to arise among them ten or twenty men, there would not be a man among them except that he would claim the Caliphate for himself. With each man among them would be ten thousand others, all of them fighting each other and charging each other with unbelief until even the believer would fear for himself, his religion, his life, his family, his wealth, and he would not know where to travel or with whom he should be.

Source: Tārīkh Dimashq 69290