The conception of an Ethiopian nation by Ethiopian nationalists is stated to have begun with the Aksumite Kingdom in the 4th century A.D.[1] The Aksumite Kingdom was a predominantly Christian state that at the height of its power controlled what is now the Ethiopian Highlands, Eritrea, and the coastal regions of Southern Arabia.[1] The Aksumite Kingdom was responsible for the development of the religious movement that became the Ethiopian Orthodox Tewahedo Church.[1] However, the expansion of Islam in the 7th century caused the decline of the Aksumite Kingdom, and most of the lowland populations converted to Islam, while the highland people remained Christian.[1] Since the Aksumite people became divided between Christian highlands and Islamic lowlands, religious and tribal tensions and rivalries between the people intensified.[1] The Aksumite society changed into a loose confederation of city-states that maintained the language of Aksum.[1]