In the 500s CE, Ethiopia invaded its cross-straits neighbor Yemen, under the pretext that the Arab Jewish King,note Abu Nuwas, was persecuting Christians. The Ethiopian hegemony lasted for about a century until the Sassanid Persians conquered that part of the Middle East. During the Ethiopian occupation of Yemen, it was said that the Christian king of Ethiopia, Kaleb, built a Church known as Al-Qualis to the Arabs living in Yemen (which is part of the Arabian peninsula). It is said that a merchant from Mecca disrespected the church, as he feared it might divert the pagan pilgrimage from Mecca to Christian-controlled lands. In retaliation, Kaleb led a force to attack Mecca, but the elephants in his army stopped short of the city and refused to attack, leading his army to turn back. This event was known as the Year of the Elephant, and was the same year Muhammad was born.
Following the rout of Ethiopian forces from the Arabian peninsula and the subsequent rise of Islam, Christian Ethiopia found itself cut off from the rest of the Christian world for roughly a millennium. During this time, legends spread in Europe of a mystical "Prester John", a Christian King from a far-off land. The Portuguese "rediscovered" Ethiopia in the 1500s, during a war against the Ottoman Turks. During this time, Ethiopia re-asserted itself as a regional power, and began to assume its present shape, while incorporating many Muslims as a significant minority as the country absorbed the lands they lived in. An Ethiopian prince, Abraham Petrovich Gannibal, came to Russia and became an ancestor of the 19th-century poet Alexander Pushkin.
During the age of colonialism, Ethiopian became the only African country besides Liberia to escape European colonization, and the only one to completely escape colonization,note when its forces won the Battle of Adowa, in which an 80,000 strong Ethiopian army defeated 20,000 Italian troops. Sadly, Ethiopia (then known as Abyssinia) was occupied by the Italians under Benito Mussolini in the 1930s, but the occupation did not last very long. An interesting note is that the leader of Ethiopia at the time, Emperor Haile Selassie (birth name Ras Tafari) became a major figure in the Rastafari Faith. Even more interestingly, he rejected godhood, but never actively tried to persuade the Rastafari from their faith, deciding (more or less), "I know I'm not God, but if these people think I am, who am I to tell them no?" He also participated in the founding of the Non-Aligned Movement along with Jawaharlal Nehru, Kwame Nkrumah, Gamal Abdel Nasser (a small miracle, since Egypt and Ethiopia have a history of not getting along that dates back centuries if not millennia), Sukarno, and Josip Broz Tito.
Ethiopia has since been involved in various power struggles in East Africa during and after the Cold War. A major regional player, Ethiopia has one of the fastest-growing populations in the world. With more than 107 million people, it has the second largest population in the continent and dwarfs virtually every country in Europe, save Russia. Ethiopia is poor and landlocked, but it is nevertheless a civilized land, producing fine coffee, being the plant's native land,note and major works of Christian art and architecture, such as churches carved out of solid rock. Not to mention the fact that it has lousy relations with almost all its neighbours, save maybe Djiboutinote and Kenya; the worst of all with Eritrea, which seceded from Ethiopia in 1991 after a 30 year-long independence struggle and for a long time considered Ethiopia's archnemesis, although relations have been thawing a good deal since the reformist Abiy Ahmed ascended as Prime Minister in 2018, with both countries exchanging ambassadors for the first time. In wider East Africa, Ethiopia has mildly good relations with South Sudan and the countries around Lake Victoria (Uganda, Burundi, Rwanda) on account of being less-developed countries that want to harness as much of the sources of the Nile as they can for development; they are opposed by Egypt and Sudan in North Africa, who are more or less utterly dependent on the Nile to support their large and growing populations and economies and need as much of its water as they can get. Compromise on the issue has been... a bit slow.
Fun fact: Ethiopia is allegedly the home of The Ark of the Covenant (this is generally beyond a doubt in the minds of the people living there). It is said to be inside a small building in the town of Axum that only a single monk is ever allowed to see. The Ethiopians believe that if anyone else should see it, they will die shortly thereafter, like in Raiders of the Lost Ark.
The Ethiopian flag