Short answers, pulled from the story.
The Ethiopian Empire was founded in 1270 by Yekuno Amlak, an Amhara nobleman who defeated the last Zagwe king at the Battle of Ansata. He claimed descent from the last Aksumite king and, through that lineage, from the biblical king Solomon, establishing the Solomonic dynasty.
The Battle of Adwa took place in 1896, when Ethiopian forces under Emperor Menelik II decisively defeated Italy during the First Italo-Ethiopian War. The victory forced Italy to sign the Treaty of Addis Ababa, recognizing Ethiopian independence and setting the borders of Eritrea. It remains one of the few instances in the 19th century of an African state defeating a European colonial power.
The empire survived through a combination of resistance by Emperor Gelawdewos and military support from Portugal. In 1541, four hundred Portuguese musketeers arrived at Massawa and, after heavy losses including the death of their commander Cristovao da Gama at Wofla, allied with Gelawdewos to defeat the imam Ahmad ibn Ibrahim al-Ghazi at the Battle of Wayna Daga, where the imam was killed and his invasion force collapsed.
The Zemene Mesafint, or Princes Era, was a period of decentralization in the Ethiopian Empire lasting from 1769 to 1855. During this time, regional lords known as Rases fought for power while emperors held only limited authority over the area around the capital Gondar. Society and culture stagnated, and religious conflict within the Ethiopian Orthodox Church and between Christians and Muslims was frequently used as a pretext for strife.
Haile Selassie presided over the formation of the Organisation of African Unity in 1963, and the organization established its headquarters in Addis Ababa. He was elected its first official chairperson. Along with Modibo Keita of Mali, Selassie helped negotiate the Bamako Accords, which ended the border conflict between Morocco and Algeria.
The empire collapsed after the government failed to respond adequately to the 1973 Wollo famine, while high fuel prices from the 1973 oil crisis and urban discontent fueled a revolt in February 1974. A military committee called the Derg formed in June 1974, and on the 12th of September 1974 it deposed and imprisoned Emperor Haile Selassie. The monarchy was formally abolished in March 1975, ending seven centuries of Solomonic rule.