Sudan (Arabic: السودان as-Sūdān Listeni/suːˈdæn/ or /suːˈdɑːn/;), officially the Republic of the Sudan (Arabic: جمهورية السودان Jumhūrīyat as-Sūdān), is an Arab republic in the Nile Valley of North Africa, bordered by Egypt to the north, the Red Sea, Eritrea and Ethiopia to the east, South Sudan to the south, the Central African Republic to the southwest, Chad to the west and Libya to the northwest. The Nile River divides the country into eastern and western halves. Its predominant religion is Islam. Sudan was home to numerous ancient civilizations, such as the Kingdom of Kush, Kerma, Nobatia, Alodia, Makuria, Meroë and others, most of which flourished along the Nile River. During the predynastic period Nubia and Nagadan Upper Egypt were identical, simultaneously evolved systems of pharaonic kingship by 3300 BC. By virtue of its proximity to Egypt, the Sudan participated in the wider history of the Near East inasmuch as it was Christianized by the 6th century, and Islamized in the 7th. As a result of Christianization, the Old Nubian language stands as the oldest recorded Nilo-Saharan language (earliest records dating to the 9th century). During Classical Antiquity, modern-day Sudan was known as Ethiopia. Sudan was the largest country in Africa and the Arab world until 2011, when South Sudan separated into an independent country, following an independence referendum. Sudan is now the third largest country in Africa (after Algeria and the Democratic Republic of the Congo) and also the third largest country in the Arab world (after Algeria and Saudi Arabia). Sudan is a member of the United Nations, the African Union, the Arab League, the Organisation of Islamic Cooperation and the Non-Aligned Movement, as well as an observer in the World Trade Organization. Its capital is Khartoum, the political, cultural and commercial centre of the nation. It is a federal presidential representative democratic republic. The politics of Sudan is regulated by a parliamentary organization called the National Assembly. The Sudanese legal system is based on Islamic law. Sudan suffers from several challenges. For much of Sudan's history, the nation has suffered from rampant ethnic strife and has been plagued by internal conflicts including two civil wars and the War in the Darfur region. Sudan suffers from poor human rights most particularly dealing with the issues of ethnic cleansing and slavery in the nation.