As recently as 2012, it appeared that Islamists could overcome their many internal dissimilarities -- sectarian (Sunni, Shi'ite), political (monarchical, republican), tactical (political, violent), or attitudes toward modernity (Salafi, Muslim Brotherhood) -- and cooperate. In Tunisia, for example, Salafis and the Muslim Brotherhood (MB) types found common ground. Differences between all these groups were real but secondary, as I put it then, because "all Islamists pull in the same direction, toward the full and severe application of Islamic law (the Shari'a)."
This sort of cooperation still persists in small ways, as shown by a recent meeting between a member of Turkey's ruling party and the head of a Salafi organization in Germany. But Islamists have in recent months abruptly and overwhelmingly thrown themselves at each others' throats. Islamists still constitute a single movement who share similar supremacist and utopian goals, but they also have different personnel, ethnic affiliations, methods, and philosophies.
Islamist internecine hostilities have flared up in many other Muslim-majority countries. Sunni vs Shi'a tensions can be seen in Turkey vs Iran, also due to different approaches to Islamism; in Lebanon, where it's Sunni vs Shi'ite Islamists and Sunni Islamists vs the army; Sunni vs Shi'ite Islamists in Syria; Sunni vs Shi'ite Islamists in Iraq; Sunni Islamists vs Shi'ites in Egypt; and Houthis vs Salafis in Yemen.