Empire. They arrived in Byzantine Syria which had a largely Aramean population. They initially settled in the Hauran region, eventually spreading to the entire Levant (modern Lebanon, Israel, Palestine and Jordan), briefly securing governorship of parts of Syria and Transjordan away from the Nabataeans. The Arab Lakhmid Kingdom was founded by the Lakhum tribe that emigrated from Yemen in the 2nd century and ruled by the Banu Lakhm, hence the name given it. They adopted the religion of the Church of the East, founded in Assyria/Asōristān, opposed to the Ghassanids Greek Orthodox Christianity, and were clients of the Sasanian Empire. The Byzantines and Sasanians used the Ghassanids and Lakhmids to fight proxy wars in Arabia against each other. History of Arabization Arabization during the early Caliphate The earliest and most significant instance of "Arabization" was the early Muslim conquests of Muhammad and the subsequent Rashidun and Umayyad Caliphates. They built a Muslim Empire that grew well beyond the Arabian Peninsula, eventually reaching as far as Iberia in the West and Central Asia to the East, covering , making it one of the largest empires in history. Southern Arabia South Arabia is a historical region that consists of the southern region of the Arabian Peninsula, mainly centered in what is now the Republic of Yemen, yet it also included Najran, Jizan, and 'Asir, which are presently in Saudi Arabia, and the Dhofar of present-day Oman. Old South Arabian was driven to extinction by the Islamic expansion, being replaced by Classical Arabic which is written with the Arabic script. The South Arabian alphabet which was used to write it also fell out of use. A separate branch of South Semitic, the Modern South Arabian languages still survive today as spoken languages in southern of present-day Saudi Arabia, Yemen, and Dhofar in present-day Oman. Although Yemen is traditionally held to be the homeland of Arabs, most of the sedentary Yemeni population did not speak Arabic (but instead Old South Arabian languages) prior to the spread of Islam. Eastern Arabia Before the 7th century CE, the population of Eastern Arabia consisted of Christian Arabs, Zoroastrian Arabs, Jews, and Aramaic-speaking agriculturalists. Some sedentary dialects of Eastern Arabia exhibit Akkadian, Aramaic and Syriac features. The sedentary people of ancient Bahrain were Aramaic speakers and to some degree Persian speakers, while Syriac functioned as a liturgical language. The Levant On the eve of the Rashidun Caliphate conquest