The Gambia (Listeni/ˈɡæmbiə/; officially the Republic of the Gambia and often called simply Gambia) is a country in West Africa. It is surrounded by Senegal, apart from a short strip of Atlantic coastline at its western end. It is the smallest country on mainland Africa. The country is situated on either side of the Gambia River, the nation's namesake, which flows through the country's centre and empties into the Atlantic Ocean. Its area is 10,689 square kilometres (4,127 sq mi) with a population of 1,882,450 at the 15 April 2013 Census (provisional). Banjul is the Gambian capital, but the largest cities are Serekunda and Brikama. The Gambia shares historical roots with many other West African nations in the slave trade, which was the key factor in the placing and keeping of a colony on the Gambia River, first by the Portuguese, during which era it was La Gambia, and later by the British. On 18 February 1965, The Gambia gained independence from the United Kingdom and joined the Commonwealth of Nations as Republic of the Gambia. It withdrew from the British Commonwealth in October 2013. Since gaining independence, Gambia has enjoyed relative political stability, with the exception of a brief period of military rule in 1994. Due to the fertile land of the country, the economy is dominated by farming, fishing, and tourism. About a third of the population lives below the international poverty line of US$1.25 a day.