Short answers, pulled from the story.
The oldest known reference to the Habesha people appears in second or third century Sabaean engravings. This ancient designation predates the modern understanding of the term by millennia and describes a group of peoples rather than a specific ethnicity.
The word Habesha may have deeper roots with Egyptian hieroglyphic references from 1450 BC under Pharaoh Hatshepsut describing a foreign people from the Land of Punt. By the fifth century CE, the late Latin form Abissensis emerged and the Greek term Abasēnoi was used to describe an Arabian people living next to the Sabaeans.
Christianity arrived in northern Ethiopia and Eritrea around the 4th century hundreds of years before most of Europe converted. These churches were founded by Syrian monks and maintained strong ties with the Coptic Orthodox Church of Alexandria until the 1950s when they gained independence.
Kassa Haile Giorgis known as Emperor Tewodros unified the realm in 1855 after a semi-anarchic period of rival warlords fighting for power. The Tigrayans briefly returned to the throne with Yohannes IV in 1872 but his death in 1889 shifted power back to the Amharic-speaking elite.
The Habesha people speak languages belonging to the Ethiopian Semitic branch of the Afroasiatic family with Ge'ez serving as the classical language of the region. Ge'ez is ancestral to Tigre and Tigrinya languages and remains used for liturgical purposes in the Eritrean and Ethiopian Orthodox Tewahedo Churches.
In the modern era the term Habesha has evolved to serve as a supra-national ethnic identifier for all Eritreans and Ethiopians particularly within diasporic populations. This broader usage acts as a counter to more exclusionary identities such as Amhara or Tigrayan though it remains contested by those who object to the obscuring of national specificity.