The early caliphate was not an especially stable place. In the two centuries after Muhammad’s death in 632, the empire went through four fitnas, or civil wars. It’s fair to say that the second of these, which lasted from 680 to 692, was really almost a do over of the first, with the same factions (the Umayyads, loyalists of Ali and his family, and those who were neither of those things) having another go at sorting out early Islam’s political future.
Today is the anniversary of an early but critical battle in that war, 684’s Battle of Marj Rahit, which was fought near Damascus between the two dominant factions that had formed among the Arab tribes, the “northern” Qays and the “southern” Yaman (or Kalb). These were relatively recent factions, created as Arab fighters sorted themselves into social groups in their newly-conquered lands. Those groupings then projected their factional solidarity back into pre-Islamic Arabian society, which was ahistorical but gave the factions real social currency. The two groups developed their own tribal customs, dress, etc., and a major, often violent, rivalry developed between them.