Fort Smith is the second-largest city in Arkansas and one of the two county seats of Sebastian County. As of the 2010 Census, the population was 86,209. With an estimated population of 87,443 In 2012, it is the principal city of the Fort Smith, Arkansas-Oklahoma Metropolitan Statistical Area, a region of 298,592 residents that encompasses the Arkansas counties of Crawford, Franklin, and Sebastian, and the Oklahoma counties of Le Flore and Sequoyah.Fort Smith has a sister city relationship with Cisterna, Italy, site of the World War II Battle of Cisterna, fought by United States Army Rangers commanded by Fort Smith native William O. Darby. The city also has a mutual friendship-city relationship with Jining, China. Fort Smith lies on the Arkansas-Oklahoma state border, situated at the confluence of the Arkansas and Poteau rivers, also known as Belle Point. Fort Smith was established as a western frontier military post in 1817, when it was also a center of fur trading.