South Sudan, officially the Republic of South Sudan, is a landlocked country in East Africa. It is bordered on the north by Sudan; on the east by Ethiopia; on the south by the Democratic Republic of the Congo, Uganda and Kenya; and on the west by Central African Republic. South Sudan's diverse landscape includes vast plains and plateaus, dry and tropical savannahs, inland floodplains, and forested mountains. The Nile River system is the defining physical feature of the country, running south to north across its center, which is dominated by a large swamp known as the Sudd. South Sudan has a population of 12.7 million. Juba is the capital and largest city.