Why is The Gambia a long and narrow country?

The Gambia’s long, narrow shape is the result of 19th-century territorial compromises between Great Britain and France.1

While Britain controlled the lower Gambia River and France ruled the surrounding colony of Senegal, the two powers engaged in a struggle for regional influence. Following a conference in Paris in 1889, France formally ceded control of the riverine areas to Britain, and the country's present-day boundaries were drawn to encompass the land on either side of the river.2134

This unique geography, which extends nearly 300 miles into the interior while remaining only 15 to 30 miles wide, reflects the British focus on securing and controlling access to the river for trade and naval purposes.321