During the late 19th century, Africa was rapidly being occupied by European colonial powers. This period in African history is usually called the Scramble for Africa. The two major powers involved in this scramble were the United Kingdom and France.
It came to pass that the French thrust into the African interior was mainly from West Africa (modern day Senegal) eastward, through the Sahel along the southern border of the Sahara, a territory covering modern day Senegal, Mali, Niger, and Chad. Their ultimate aim was to have an uninterrupted link between the Niger river and the Nile, hence controlling all trade to and from the Sahel region, by virtue of their existing control over the Caravan routes through the Sahara.
The British, on the other hand, wanted to link their possessions in Southern Africa (modern South Africa, Botswana, Zimbabwe, and Zambia), with their territories in East Africa (modern Kenya), and these two areas with the Nile basin. Sudan (which in those days included modern day Uganda) was obviously key to the fulfillment of these ambitions, especially since Egypt was already under British control. This 'red line' through Africa is made most famous by Cecil Rhodes.
When one draws a line from Cape Town to Cairo (Rhodes' dream), and one from Dakar to the Horn (the French ambition), these two lines intersect somewhere in eastern Sudan near Fashoda, explaining its strategic importance. In short, Britain had sought to extend its East African empire contiguously from Cairo to the Cape of Good Hope, while France had sought to extend its own holdings from Dakar to the Sudan, which would enable its empire to span the entire continent from the Atlantic Ocean to the Red Sea.
A French force under Jean-Baptiste Marchand arrived first at the strategically located fort at Fashoda soon followed by a British force under Lord Kitchener, commander in chief of the British army since 1892. The French withdrew after a standoff, continued to press claims to other posts in the region. In March 1899 the French and British agreed that the source of the Nile and the Congo rivers should mark the frontier between their spheres of influence.