The bloggers at Coming Anarchy have put together an informative series of posts about the shifting borders of states and empires. There’s a time-lapse animation of …

http://www.newadvent.org/cathen/12400b.htm

A brief excerpt from chapter one of my book:

...The Himyar [an important south Arabian tribe that predated the Christian era and reached its peak beginning circa 299 AD] then began enlarging their power, to the point of being able to claim the title of kingship over both central and coastal Arabia. They used the Hujr clan of the tribe of Kinda as a satellite to control the center, and lesser tribes elsewhere, including the area north of the trading city of Mecca. This expansion naturally brought them within the realm of international politics. Byzantium began cultivating Kinda as a satellite, and through its influence with Ethiopia, began to intervene in Arabia itself in order to protect Christian missionaries and communities. Kinda was key because it controlled the territory containing trade routes linking south and eastern Arabia with Iraq (itself and old Arabic word for Mesopotamia). The Himyar established formal relations with major cities in Iraq and Persia, and in the fourth century concluded a formal peace treaty with Ethiopia. By the early sixth century, however, Christianity was perceived to be an extension of Byzantine imperial power, and war broke out between the Himyar and Ethiopia. Ethiopia was victorious, and successfully installed a Christian king over the Himyar. Around the same time the strength of the Jewish tribes was increasing, and with his death they were able to take power.

Reports of aggressions against Christian communities again brought Ethiopian intervention, who again installed a Christian King, Esimiphaeus, a Himyarite by birth, over the tribe. His Christian successor was one Abraha, a slave of a Roman merchant, whose power was sufficiently secure to quell a revolt among the Kinda and orchestrate two campaigns to subdue rebellious elements in central Arabia. One of the latter appears to be the Attack of the Elephant referred to in the Quran (105), which may have taken place the year of Muhammad’s birth. The growth of Byzantine and Jewish power increased monotheistic influence in a region that had been overwhelmingly polytheistic.

The final chapter in the story of the Himyar prior to the rise of Islam was that of Persian conquest. By AD 559 resentment toward Ethiopian rule became so great that one Sayf ibn Dhi Yazan appealed to Persia for help. The Persian ruler Khosro agreed to send an army in exchange for annual tribute. After Yazan was installed as king he was killed by Ethiopian slaves, and the Persian army returned, this time bringing southern Arabia under formal Persian rule. And so it remained an adjunct of the Persian Empire until the time of Muhammad.