The kingdom of Aksum began to convert to Christianity circa 330-340 AD. Traditional ecclesiastical accounts credit the conversion of King Ezana to the missionary efforts of Frumentius, a sailor from Tyre and christian convert who was shipwrecked on the coast of Aksumite territory. this journal article (pdf warning) goes into aspects of the sea-borne merchant trade that supported or encouraged christian evangelization in the red sea area.

It is important to note that Aksum in this period from 100 AD-650 AD was deeply connected to trade passing through the Red Sea, and Aksumite traders traveled through the Indian ocean as far as Sri Lanka.

I'm not sure which Persian war you are talking about, there were several. In any case, it is true that Aksum worked in concert with Byzantium, and Aksum engaged in military expeditions in Yemen and the Arabian peninsula which had the ultimate object of supporting Arab christians and weakening Persian influence in Yemen. In Foundations of an African Civilization, DW Phillipson assesses the claims of Procopius that the Aksumite invasion of the Himyar kingdom (in what is now Yemen) in 525 AD was encouraged by Byzantine emperor Justinian, and that Byzantine interests were to secure trade routes, particularly access to silk, through the Red Sea and into the Indian ocean that did not go through Persian territory.

However, Himyar was later conquered by Persia 50 years later, circa 575. Stuart Munro-Hay characterizes the period from 575-628 as a difficult one where Aksum had lost it's overseas possessions in Yemen, and was now confronted with a possibly vengeful Persian client. Munro-Hay speculates that it may have been Persian naval pressure and the Persian occupation of Egypt from 619-28 that strangled Aksumite trade and led to the kingdom's decline.

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Foundations of an African Civilization; Aksum and the Northern Horn 1000 BC- 1300 AD by David W Phillipson. pp 50.

Aksum; an African Civilization of Late Antiquity by Stuart Munro-Hay. pp 58.