From 300 AD until the advent of Islam in Yemen

This period witnessed a lot of disorder and turmoil. The great many foreign and civil wars cost the people of Yemen their independence. During this era, the Aksumites invaded Tihama & Najran for the first time in 340 AD, making use of the constant intra-tribal conflict of Hamdan and Himyar. The Aksumite occupation of Tihama and Najran lasted until 378 AD, whereafter Yemen expelled the Aksumites. After the Ma'rib Dam last Great Flood (450 or 451 AD) weakened Himyar further and led to its collapse.
In the fifth century, several kings of Himyar are known to have converted to Judaism. The political context was the position of Arabia between the competing empires of Christian Byzantium and Zoroastrian Persia. Neutrality, and good trade relations with both empires, was essential to the prosperity of the Arabian trade routes. Scholars speculate that the choice of Judaism may have been an attempt at maintaining neutrality.^[3]
As the story has come down to us, about the year 500 AD, the King of Himyar, Abu-Kariba Assad, undertook a military expedition into northern Arabia in an effort to eliminate Byzantine influence. The Byzantine emperors had long eyed the Arabian Peninsula as a region in which to extend their influence, thereby to control the lucrative spice trade and the route to India. Without actually staging a conquest of the region, the Byzantines hoped to establish a protectorate over the pagan Arabs by converting them to Christianity. The cross would then bear commercial advantages as it did in Ethiopia. The Byzantines had made some progress in northern Arabia but had met with little success in Himyar.^[3]
Abu-Kariba's forces reached Yathrib and, meeting no resistance and not expecting any treachery from the inhabitants, they passed through the city, leaving a son of the king behind as governor. Scarcely had Abu-Kariba proceeded farther, when he received news that the people of Yathrib had killed his son. Smitten with grief; he turned back in order to wreak bloody vengeance on the city. After cutting down the palm trees from which the inhabitants derived their main income, Abu-Kariba laid siege to the city. The Jews of Yathrib fought side by side with pagan fellow inhabitants to defend their town and harried the besiegers with sudden sallies. During the siege Abu-Kariba fell severely ill. Two Jewish scholars in Yathrib, Kaab and Assad by name, hearing of their enemy's misfortune, called on the king in his camp, and used their knowledge of medicine to restore him to health. While attending the king, they pleaded with him to lift the siege and make peace. The sages' appeal is said to have persuaded Abu-Kariba; he called off his attack and also embraced Judaism along with his entire army. At his insistence, the two Jewish savants accompanied the Himyarite king back to his capital, where he demanded that all his people convert to Judaism. Initially, there was great resistance, but after an ordeal had justified the king's demand and confirmed the "truth" of the Jewish faith, many Himyarites embraced Judaism. The conversions, however, were not total, and there remained as many pagans as Jews in the land. Such conversions, by ordeal, were not uncommon in Arabia. Some historians argue that the conversions occurred, not due to political motivations, but because Judaism, by its philosophical, simplistic and austere nature, was attractive to the nature of the Semitic people. In any case, it is known that by the 6th and 7th centuries, Judaism flourished in Himyar; and in inscriptions dating from those centuries Jewish religious terms such as "Rahman" ("the merciful," a divine epithet), "the god of Israel", and the "Lord of Judah" bears testament to this fact.^[3]
Abu-Kariba's reign did not last long after his conversion to Judaism. His warlike nature prevented him from maintaining peace and prompted him to engage in bold enterprises. It is uncertain how Abu-Kariba met his death, although some scholars believe that his own soldiers, worn out by constant campaigning, killed him. He left three sons, Hasan, Amru, and Zorah, all of whom were minors at the time. After Abu-Kariba's demise, a pagan named Dhu-Shanatir seized the throne.^[3]

• Himyar: The most famous of whose septs were Zaid Al-Jamhur, Banu Quda'a and Sakasic.
• Kahlan: The most famous of whose septs were Hamdan, Azd, Anmar, Tayy, Shammar, Midhhij, Kinda, Lakhm, Judham

Kahlan septs emigrated from Yemen to dwell in the different parts of the Arabian Peninsula prior to the Great Flood (Sail Al-‘Arim of Ma’rib Dam), due to the failure of trade under the Roman pressure and domain on both sea and land trade routes following Roman occupation of Egypt and Syria.
Naturally enough, the competition between Kahlan and Himyar led to the evacuation of the first and the settlement of the second in Yemen.
The emigrating septs of Kahlan can be divided into four groups:

• Azd: Who, under the leadership of ‘Imran bin ‘Amr Muzaiqbâ’, wandered in Yemen, sent pioneers and finally headed northwards. Details of their emigration can be summed up as follows:
  • Tha‘labah bin ‘Amr left his tribe Al-Azd for Hijaz and dwelt between Tha‘labiyah and Dhi Qar. When he gained strength, he headed for Madinah where he stayed. Of his seed are Aws and Khazraj, sons of Haritha bin Tha‘labah.
  • Haritha bin ‘Amr, known as Khuza‘a, wandered with his folks in Hijaz until they came to Mar Az-Zahran. , they conquered the Haram, and settled in Makkah after having driven away its people, the tribe of Jurhum.
  • ‘Imran bin ‘Amr and his folks went to ‘Oman where they established the tribe of Azd whose children inhabited Tihama and were known as Azd-of-Shanu’a.
  • Jafna bin ‘Amr and his family, headed for Syria where he settled and initiated the kingdom of Ghassan who was so named after a spring of water, in Hijaz, where they stopped on their way to Syria.

• Lakhm and Judham: Of whom was Nasr bin Rabi‘a, father of Manadhira, Kings of Heerah.

• Banu Tai’: Who also emigrated northwards to settle by the so- called Aja and Salma Mountains which were consequently named as Tai’ Mountains.

• Kindah: Who dwelt in Bahrain but were expelled to Hadramout and Najd where they instituted a powerful government but not for long, for the whole tribe soon faded away.

Another tribe of Himyar, known as Banu Quda'a, also left Yemen and dwelt in Samawa semi-desert on the borders of Iraq.