A little different history of the Crusades with a little different circumstances during the Third Crusade, leading to the successful Crusade against Egypt, which leads to the establishment of the Latin Kingdom of Egypt, and re-establishment of contact between Ethiopia and the Latin West, Ethiopia keeps its own rites but pledges allegiance to the Pope (ala a few Middle Eastern sects during the Crusades).
Maybe a crusading order is founded down in Ethiopia, ala Teutonic Knights, to keep European knights coming down to Ethiopia (which the Italian merchant cities support to keep the Red Sea and Horn of Africa open to trade).
Ethiopia extends its control into the Horn of Africa, and with the aid of the Egyptian-Norman fleet takes Aden. Ethiopia is able to successfully unify with the added military help from Europeans and improved revenue from trade taxes.