Yaman was an Arab tribal confederation, originating from South Arabia, known for their centuries-long rivalry with the Qays, another Arab tribal confederation. As late as the nineteenth century battles were fought in Palestine between Qays and Yaman groups.
The Yamanis supported the Umayyads which was integral to them coming to power in the first Muslim civil war (fitna) from 656 to 661 and to them regaining power in the second Muslim civil war from 683 to 692.
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The Qays–Yaman rivalry refers to the rivalry between the tribal factions of Qays–Mudar and the Yaman. The history of the rivalry centers mainly within the armies and administrations of the Umayyad Caliphate in the 7th and 8th centuries, but persisted to varying degrees among the Arabs through Ottoman rule (1517–1918). Membership in either faction was rooted in the genealogical origins of the tribes, real or perceived, which divided them into south Arabian descendants of Qahtan (the Yaman) or north Arabian descendants of Adnan (Qays–Mudar).
The tribes which constituted the Yaman, most prominently the Kalb, Ghassanids, Tanukh and Judham, were well-established throughout the Syria (the Levant) since the pre-Islamic period, while the Qaysi tribes, namely the Sulaym, Banu Amir and Ghatafan migrated to northern Syria and Upper Mesopotamia with the Muslim armies in the 7th century. The feud did not effectively take shape until after the reign of Caliph Mu'awiya I (r. 661–680), who, along with his Sufyanid descendants, were tied to the Kalb, the leading tribe of Yaman, through marriage and military dependence. When the last Sufyanid caliph died in 684, the Kalb and its allies resolved to ensure continued Umayyad rule to maintain their stately privileges, while the Qays backed Abd Allah ibn al-Zubayr's bid for the caliphate. That year, the Kalb routed the Qays at the Battle of Marj Rahit, leading to years of revenge-driven, tit-for-tat raids known as ayyam (days) because the battles were typically day-long affairs.
The Battle of Marj Rahit (Arabic: يوم مرج راهط, romanized: Yawm Marj Rāhiṭ) was one of the early battles of the Second Fitna. It was fought on 18 August 684 between the Kalb-dominated armies of the Yaman tribal confederation, supporting the Umayyads under Caliph Marwan I, and the Qays under al-Dahhak ibn Qays al-Fihri, who supported the Mecca-based Abdallah ibn al-Zubayr; the latter had proclaimed himself Caliph. The decisive Umayyad victory consolidated their power over Bilad al-Sham (the Islamic Levant), paving the way for their eventual victory in the war against Ibn al-Zubayr. However, it also left a bitter legacy of division and rivalry between the Qays and the Yaman, which would be a constant source of strife and instability for the remainder of the Umayyad Caliphate.