 The political situation was extremely fluid and the boundaries of the various emirates and sultanates tended to disappear quickly.In the Umayyad period, large tribes of nomads from the "Hanifa", "Tamim", and "Abd al-Qays" tribes crossed the Persian Gulf and occupied some of the richest Basran territories around Ahvaz and in Fars during the second Islamic civil war in 661-665/680-684 (Encyclopædia Iranica, p. 215, under "Arab Tribes of Iran").During the Abbassid period, in the second half of the 10th century, the "Assad" tribe, taking advantage of quarrels under the Buwayhids, penetrated into Khuzestan, where the "Tamim" tribe had been inhabiting since pre-Islamic times.