How did the Gambia River shape the borders of The Gambia?

The borders of The Gambia are a direct result of 19th-century colonial territorial compromises between Great Britain, which controlled the lower Gambia River, and France, which governed the surrounding territory of Senegal.1

Rather than following natural geographic or ethnic lines, the country's narrow, elongated shape—extending roughly 300 miles into the interior while maintaining a width of only 15 to 30 miles—was defined by the British desire to maintain control over the riverine trade routes. Following a conference in Paris in 1889, France formally ceded control of the river to Britain, and the current boundaries were drawn to encompass the land on either side of the river's path. This unique configuration leaves the nation almost entirely surrounded by Senegal, with the exception of its short Atlantic coastline.213