I'm curious as to what influence the Axumites had over Southern Arabia. Did they ever completely conquer it, or were they limited to trade? Did they ever get close to sacking Mecca, as I've heard some people claim?
Sure. My primary source can be read in its entirety
here.
Aksumite influence in Yemen began in the early third century. At that time, there were three kingdoms vying for dominance on the region. Himyar, located in the southern corner of the area with its capital at Zafar; Hadhramawt, located to the east of Himyar along that coast with its capital at Shabwa; and Saba', located somewhat to the north, between Himyar and Hadhramawt, with its capital at Marib. Sometime between 200 and 210, Aksum and Saba' entered into an alliance against Himyar, whom had a strong influence on the Red Sea trade that Aksum wanted for itself.
The exact sequence of events is muddy, but it appears that Saba' was victorious against Himyar. Aksum garrisoned the Himyarite capital, Zafar, and installed a governor,apparently making it a tributary province. The Sabaean king died in 210 and was succeeded by his son, Sha'ir Awtar, who was co-ruled with his brother for a time. This period was apparently relatively peaceful, with Himyar subdued and Hadhramawt kept peaceful after its king married the sister of Awtar. Awtar even helped the the king of Hadhramawt but down a rebellion in 217-18.
During these years however, the influence of Aksum, which had learned to play off the Yemeni tribal kingdoms against each other, must have grated the native peoples. In 225, King Awtar of Saba' invaded Hadhramawt and seize their capital. He also expelled the Aksumite garrison Zafar. Some sort of peace seemed to last from 230-240, after which new hostilities opened.
Sorry I got to run, just read that PDF and you'll get a good summary of events
From pg.80 of that source sums up the cause of Kaleb's invasion fairly well.
Kaleb invaded the Yemen around 520, in order to oust the Jewish Himyarite king Yusuf Asar Yathar, who was persecuting the Christian population. This ostensible reason for mounting the expedition across the Red Sea probably covers a number of other causes, since it seems that Yusuf may have also acted against Aksumite interests, and those of her Roman allies, in the political and commercial spheres.
Upon the declaration of war, if not sometime before, Yathar had destroyed the Abyssinian church and killed the Aksumites in Zafar. The Aksumites, lead by a general named Hiuna, landed on the coast and marched to Zafar, where they defeated Yathar's forces. A christian governor by the name of Sumyafa` Ashwa` was installed, and ruled for five years until being overthrown by Abreha in 525. Kaleb sent a force of three thousand men, but that army defected. Another army was defeated by Abreha. After that, the Aksumites did not try to directly interfere in Yemen again.
Would anybody be interested in a map series?