Kahlan was one of the main tribal federations of Saba'a in Yemen.
By the 2nd century BCE Saba'a was declining gradually and its southern neighbor Himyar was able to settle many Nomadic tribes that were allied to Himyar and create a stronger Himyarite nation in the lowlands. Eventually Saba'a was incorporated into Himyar and resistance was reduced to the Kahlan tribes who were overpowered by Himyar and forced out of Highlands in Yemen. Most Of Kahlan remained in the Yemeni desert region around Marib until the destruction of the Dam in the 3rd century CE. this forced the Kahlani tribes to emigrate northwards through Arabia. They reaching as far as Mesopotamia and Syria prior to the 7th Century Arab conquests under Islam. After the Arab conquests, the Kahlani Arabs, among other Qahtani and Adnani tribes, reached all the way to the far edges of the Umayyad Empire.
The Kahlan branched into 5 main branches; Azd, Hamdan, Lakhm, Tayy, Kindah.
In the 3rd century AD. The Azd branched into four branches each led by one of the sons of Amr bin Muzaqiba
Imran bin Amr and the bulk of the tribe went to Oman where they established the Azdi presence in Eastern Arabia and later invaded Karman and Shiraz in Southern Persia. Another branch headed west back to Yemen and a group went further West all the way to Tihama on the Red Sea. This branch will become known as Azd Uman after Islam.
Jafna bin Amr and his family, headed for Syria where he settled and initiated the kingdom of the Ghassanids who was so named after a spring of water where they stopped on their way to Syria.