Two Arabian dynasties stand out very distinctly during the Byzantine period. One, the dynasty of the Ghassanids in Syria, Monophysitic in its religious tendencies and dependent upon the Byzantine emperors, became particularly powerful in the sixth century under Justinian, when it aided the Byzantine Empire in its military undertakings in the East. This dynasty probably ceased to exist in the early seventh century, when the Persians conquered Syria and Palestine. The second Arabian dynasty, the Lakhmids, centered in the city of Hira on the Euphrates. Because of its vassal relations with the Persian Sassanids it was hostile to the Ghassanids. It also ceased at the beginning of the seventh century. In the city of Hira Christianity, in its Nestorian form, had a body of adherents, and even some members of the Lakhmid dynasty accepted it. Both dynasties had to defend the borders of their kingdom, the Ghassanids on the Byzantine side and the Lakhmids on the Persian. Apparently both vassal states disappeared at the beginning of the seventh century, so that at the time of Muhammed's advance there was not a single political organization within the confines of the Arabian peninsula and the Syrian desert which could be called a state. There had existed in Yemen since the end of the second century B.C. the kingdom of the Sabaeans-Himyarites (Homerites). But in about the year 570 Yemen was conquered by the Persians.
Before the time of Muhammed the ancient Arabs lived in tribal organizations. Blood relationship was the only basis for common interests, which were confined almost exclusively to loyalty, protection, aid, and revenge upon enemies for insults suffered by the tribe. The least occasion sufficed for starting lasting and bloody struggle between tribes. References to these ancient times and customs have been preserved in old Arabic poetry, as well as in prose tradition. Animosity and arrogance were the two predominant elements in the mutual relations of different tribes of ancient Arabia.