Finally and most important of all, the new immigration brought Islam, the unifying force which played so significant a part in the sixteenth-century conquest of Abyssinia, and which remains the living faith of the Somali and of many of the peoples of present-day Ethiopia. At the same time, indirectly if not always directly, the absorption of Arab settlers seems to have given an impetus to, or to have precipitated, the movements of expansion of the Somali and Oromo.

I.M. Lewis, I. M. Lewis, A Modern History of the Som…, loc. 85