Arabs are a major pan-ethnic group. They primarily inhabit Western Asia, North Africa, parts of the Horn of Africa, and other areas in the Arab world. Arabic-speaking populations in general are a highly heterogeneous collection of people, with different ancestral origins and identities. The ties that bind the Arab peoples are a veneer of shared heritage by virtue of common linguistic, cultural, and political traditions. As such, Arab identity is based on one or more genealogical, linguistic or cultural grounds, although competing identities often take a more prominent role based on considerations including regional, national, clan, kin, sect, and tribe affiliations and relationships. If Arab panethnicity is regarded as a single population, then it constitutes one of the world’s largest groups after the Han Chinese. The Arabian Peninsula itself was not entirely originally Arab. Arabization occurred in some parts of the Arabian Peninsula. For example, the language shift to Arabic displaced the indigenous South Semitic Old South Arabian languages of modern-day Yemen and southern Oman. These were the languages spoken in the civilisations of Sheba, Ubar, Magan, Dilmun, and Meluhha—which were spread via migrants from the Arabian peninsula, together with written script, in the 8th and 7th centuries BC to the Horn of Africa (Ethiopia, Eritrea, Djibouti, and Somalia).