In order to understand the main reasons outlining Ethiopia's plunge into the middle ages, conditions related to factors involving Ethiopian interests prior to the new era must be studied. In the case of the Ethiopian regional interests, it must be noted that during much of the 5th and 6th centuries, Ethiopia served as a national interface between the two eastern superpowers of the time – namely Byzantium and Persia. The Aksum-based emperors of Ethiopia at this time were also very eager to establish a link with their long-time Christian counterparts in Greece and Istanbul (modern-day Turkey). During this time, many Christian merchants of Byzantinian citizenship were also bringing a good deal of wealth to that region, which increased the inclination of the aristocratic Aksumite population to favor the Byzantinians. Much trade was also done between Ethiopia and India, by way of the Ethiopian port Adulis.
The emperors of Ethiopia were, at this time, also enjoying sovereignty over vast regions in southwestern Yemen. Since this area was also tributary to the emperors, it was in their best interest to keep the rather distant under check.
In 527 CE, the peace treaty between Byzantium and Persia was broken as war was declared on both sides. In an effort to enlist the aid of co-religionists in the Middle East, the Byzantinian emperor Justinian I sent embassies as far as India. In 531 CE, Julian, a Byzantinian magistrate in Alexandria, Egypt, visited Emperor Kaleb of Ethiopia bearing a message from Julian I himself. The message informed emperor Kaleb of a newly converted Jewish king, Dhu Numas, whom may possibly be conducting secessionist activities in his region of south Arabia.
Bearing in mind that emperor Julian I would only be acting for the purpose of fueling his own interests, emperor Kaleb still acted as if they were presumably on the same side. He therefore immediately dispatched notices to his regions in southern Arabia ordering that preparations should be made for war. It is also believed that Kaleb rented 62 ships from Byzantine controlled ports in the Red Sea (then known as the Erythrean Sea). Following this, approximately 120,000 soldiers were dispatched over a rather short period in order to annihilate any insurrection activity.
However, an epidemic was coincidentally circulating throughout the southern half of the Arabian Peninsula, of which the Ethiopian forces were unaware. Although very little is known regarding the epidemic itself or its origin, it seemed to have had profound effects, during the long run, on the political configuration of that area. Some historians have asserted that up to 50% of the Ethiopian ground force could have been killed as a result of this epidemic.
Even at such a high cost, the initial mission of resubjugating king Dhu Numas was finally accomplished, or as ambassador Julian himself put it: "(emperor Kaleb) himself went off against Persian territory and pillages all of it in that area. After conquering, (emperor Kaleb) gave Julian a kiss of peace on the head and sent him off with a large retinue and many gifts.”