Most nations are a bigger coming together of formerly warring subgroups. This is true of Saudi Arabia, the United States, Germany, the United Kingdom, China and smaller countries like Eritrea. Italian Eritrea was formed in 1890, just eight years after the first Italian settlements in the area, and five years after the Berlin Conference. The first lands were bought from Sultans for commercial interests before the Italian government took control.
Most smaller groups on the west coast of the Red Sea were under the Egyptian Control. They were notionally under control of the Ottoman Empire, but acted more and more independently. The big powers of the area were thrown into chaos with the Ethiopia-Egypt war and the rise of the Mahdi in Sudan. The Italians swooped in incorporating various Kingdoms and Sultanates into a colony. That lasted 62 years.
Ethiopia was the one African country which completely resisted the Scramble for Africa. It also had imperial ambitions of its own and annex Eritrea and Italian Somaliland. In 1950, Eritrea was federated with Ethiopia. Ethiopian Emperor Haile Selassie then annexed the area in 1962 leading to a 30 year war. A 1993 referendum resulted in independence. The country has a population of 6.4 million with no official language, a number of ethnic groups and a roughly 50/50 split between Muslims and Christians. The working languages are Tigrinya, Arabic and English.