How did Britain and France help create the present-day borders of The Gambia?

The present-day borders of The Gambia were established through territorial compromises between Great Britain and France during the 19th century.1

While Britain had long maintained control over the lower Gambia River to facilitate trade and suppress the slave trade, France held authority over the surrounding colony of Senegal. The specific boundaries were finalized following a conference held in Paris in 1889, during which France formally ceded control of the river to Britain. This agreement resulted in the country's distinct, narrow shape, which follows the course of the river while being otherwise surrounded by Senegalese territory.213